GB2607657A

GB2607657A - Piston compression pulse spray dryer

Info

Publication number: GB2607657A
Application number: GB2202706.4A
Authority: GB
Inventors: Stephen Bell Ian
Original assignee: Individual
Current assignee: Individual
Priority date: 2022-02-25
Filing date: 2022-02-25
Publication date: 2022-12-14
Also published as: GB202202706D0

Abstract

A piston compressor for a pulse spray dryer comprises a reciprocating piston 406 mounted within a cylinder 404 to form a compression chamber 428. An inlet and outlet valve 416, 486 are operated by a timing device to allow gas to enter and exit the compression chamber. The outlet valve may be opened and closed depending on the position of the piston in the cylinder using a U-shaped passage 448 through the piston communicating with an outlet 446 through a wall of the cylinder. The inlet valve may be opened and closed depending on the direction of movement of the piston in the cylinder using a valve disk 430, 432 movably mounted within a valve chamber 418 within the piston, with a passage 424 extending between the valve chamber and the compression chamber. Separate, electrically controlled inlet and outlet valves (600, 602, figure 6A) or a single, combined inlet and outlet valve (700, figure 7A) may instead be operated by a timing device to allow gas to enter and exit the compression chamber. A method of desalinating a salt solution such as sea water uses a piston compression pulse spray dryer which includes the piston compressor.

Description

PISTON COMPRESSION PULSE SPRAY DRYER

The present invention relates to a piston compressor and, more in particular, to the use of a piston compressor in a piston compression pulse spray dryer and to the use of a piston compression pulse spray dryer to desalinate salt water.

A problem with existing designs of desalination apparatus is that they are complex in their construction and are expensive to operate. Often, the apparatus requires constant monitoring and regular servicing by trained personnel using specific service parts. Such apparatus can utilise a number of different types of desalination technology such as solar distillation, natural evaporation, vacuum distillation, thermal distillation, multi-stage flash distillation, multiple-effect distillation, vapor-compression distillation, wave-powered distillation, membrane distillation, forward and reverse osmosis, freeze-thaw desalination and electrodialysis membranes.

Typically, such apparatus is constructed to operate on an industrial scale. Whilst that is advantageous for providing drinking water for a large population, such as a town or a city, it is often not practical for use in situations where a small-scale operation is required, such as on a farm.

Many known solutions for desalination focus on the efficiency of the system i.e. the amount of energy put in versus the amount of desalinated water extracted. This leads to complex solutions. Again, whilst this may be acceptable on apparatus used on an industrial scale, it hinders the use of such apparatus in small operations, especially where the personnel operating such apparatus are often not trained to use such apparatus and the operation of such apparatus is not the personnel's primary function.

The present invention is intended to provide a predominantly mechanical device, and ideally, a purely mechanical device which can desalinate salt water. A predominantly or purely mechanical device would be easy and cheap to construct and operate. It is intended to minimise the number of component parts, thus providing reliability and minimising the need to repair. Such a design can also be made small for use in small scale operations.

The present invention comprises a piston compressor in a piston compression pulse spray dryer to desalinate salt water. The advantage of such a device is that it can be made to have a purely mechanical construction or a substantially mechanical construction. Such a device can be made to be easy to operate and require minimal maintenance and repair.

Three pieces of relevant prior art will now be briefly described with reference to Figures 1to 3.

The first piece of prior art is a spray drying apparatus will now be described with reference to Figure 1.

Spray drying is commonly used in the production of food stuffs or pharmaceuticals for the extraction of solids from a fluid. Examples of solids are salts or chemicals dissolved in the fluid or a powdered solid suspended in the fluid. The solids are extracted from the fluid by, first, atomizing the fluid containing the solid by passing it through an atomizer and then, second, spraying the atomised fluid and solids into a hot drying gas medium, for example, air. The atomised fluid is then rapidly evaporated and subsequently separated from the solids. The solids are then collected. The evaporated fluid can then be condensed to form a liquid again. The spray drying process provides a rapid, continuous, cost-effective, reproducible and scalable process for the extraction of solids from a fluid.

Figure 1 shows a schematic diagram of a spray drying apparatus to show the basic principles of the construction of the spray drying apparatus.

Referring to Figure 1, the spray drying apparatus comprises a tank 100 in which is inserted the fluid 102 containing the solids. A first pipe 104 connects the tank 100 to a pump 106. A second pipe 108 connects the pump 106 to a housing 110 which forms a mixing chamber 112. The second pipe 108 passes through the wall of the housing 110 and extends into the mixing chamber 112. A nozzle 114 is attached to the end of the second pipe 108 inside of the mixing chamber 112.

An air pump 116 is attached to a third pipe 118. The third pipe 118 connects between the air pump 116 and an air heater 120. A fourth pipe 122 attaches between the air heater 120 and the housing 110 of the mixing chamber 112, the end of the fourth pipe 122 connecting to an aperture 124 formed through the wall of the housing 110.

A fifth pipe 126 attaches between the housing 110 of the mixing chamber 112 and a cyclonic separator 128, one end of the fifth pipe 126 connecting to an aperture 127 formed through the wall of the housing 110, the other end of the fifth pipe 126 connecting to an aperture 125 formed through the wall of the cyclonic separator 128.

The cyclonic separator 128 has a separation chamber 130 which tapers at its lower end to a sixth solids exit pipe 132. A seventh vapour exit pipe 134 connects to an aperture 136 formed through an upper part of the wall of the cyclonic separator 128.

The operation of the spray drying apparatus will now be described.

In use, the air pump 116 sucks in air from the surrounding atmosphere into the third pipe 118. The air is blown through the third pipe 118 and into the air heater 120. The air passes through the air heater 120 where it is heated to a high temperature. The heated air is then blown through the fourth pipe 122, through the aperture 124 and into the mixing chamber 112.

The tank 100 is filled with a fluid 102 containing the solids. The fluid 102 containing the solids then flows into the pump 106. The pump 106 then pumps the fluid 102 with the solids at high pressure through the second pipe 108 and the nozzle 114 and into the mixing chamber 112. As the fluid 102 with the solids passes through the nozzle 114, the fluid 102 is atomized into a spray 138. The spray 138 mixes with the heated air where it is rapidly heated, the fluid 138 vaporising as it does so. The vaporised fluid 102 and solids then pass out of the mixing chamber 112 through the fifth pipe 126 and into the separating chamber 130 where it is rotated rapidly to cyclonically separate the solids from the vaporised fluid 102. The solids then exit the separation chamber 130 through the sixth solids exit pipe 132. The vaporised fluid 102 then exits the separation chamber 130 through the seventh vapour exit pipe 134 where the vaporised fluid 102 can be cooled to return it to a liquid.

The second piece of prior art is a pulse combustion spray dryer which will now be described with reference to Figure 2.

Figure 2 shows a schematic diagram of a pulse combustion spray dryer to show the basic principles of the construction of the pulse combustion spray dryer.

A pulse combustion spray dryer comprises a pulse combustor which produces a series of pulses of hot exhaust gases and a pulse spray dryer.

Referring to Figure 2, the pulse spray dryer comprises a tank (not shown) in which is inserted the fluid containing the solids. A first pipe 204 connects the tank to a pump 206. A second pipe 208 connects the pump 206 to a housing 210 which forms a mixing chamber 212. The second pipe 208 passes through the wall of the housing 210 and extends into the mixing chamber 212. A nozzle 214 is attached to the end of the second pipe 208 inside of the mixing chamber 212.

Mounted on top of the housing 210 is a pulse combustor 250 comprising an inner wall 252 and an outer wall 254. The inner wall 252 forms a combustion chamber 256. The combustion chamber 256 is connected to the mixing chamber 212 via a third pipe 258. Mounted on the top on the inner wall 252 is a valve 260. The top of the valve 260 is connected to a fourth pipe 262 through which a combustible fuel is fed into the valve 260.

An air filter 264 is connected to an air pump 216 via a fifth pipe 266. The air pump 116 is attached to a sixth pipe 218, The sixth pipe 218 connects between the air pump 216 and the outer wall 254. When the air pump 216 is activated, air is drawn from the environment into the filter 264, through the fifth pipe 266, through the air pump 216, through the sixth pipe 218 and into a separation chamber 268 formed between the inner wall 252 and the outer wall 254. Air in the separation chamber 268 is in direct contact with side of and capable of being drawn into the valve 260.

The valve 260 injects a mixture of the combustible fuel and air into the combustion chamber 256 at pre-determine time intervals.

Mounted inside the combustion chamber 256 is a spark plug (not shown) or some other type of ignition device. After the valve 260 injects a mixture of the combustible fuel and air into the combustion chamber 256 at pre-determine time intervals, the spark plug ignites the fuel/air mixture inside of the combustion chamber 256.

The pulse spray dryer further comprises a seventh pipe 226 which attaches between the housing 210 of the mixing chamber 212 and a cyclonic separator 228, one end of the seventh pipe 126 connecting to an aperture formed through the base wall of the housing 210, the other end of the seventh pipe 226 connecting to an aperture formed through the wall of the cyclonic separator 228.

The cyclonic separator 228 has a separation chamber 230 which tapers at its lower end to an eighth solids exit pipe 232.

A ninth vapour exit pipe 234 connects to an aperture formed through an upper part of the wall of the cyclonic separator 228 to an aperture formed through a lower part of a wall of a condenser 270. The condenser 270 forms a condensing chamber 272 which has a tapered section 274 at its lower end where it connects to a tenth liquid exits pipe 276.

An eleventh air exit pipe 278 connects between the top of the condenser 270 and an exit fan 280. A twelfth pipe 282 connects between the exit fan and an exhaust duct 284.

The operation of the pulse combustion spray dryer will now be described.

Combustible fuel is fed into the valve 260. The air pump 216 draws air into the filter 264, through the fifth pipe 266, through the air pump 216, through the sixth pipe 218, into the separation chamber 268 formed between the inner wall 252 and the outer wall 254 and then into the valve 260. The valve 260 then injects a mixture of combustible fuel and air into the combustion chamber 256 at pre-determine time intervals. After the valve 260 injects a mixture of the combustible fuel and air into the combustion chamber 256 at pre-determine time intervals, the spark plug ignites the fuel/air mixture inside of the combustion chamber 256 to generate a series of combustions, which in turn produce a series of pulses of hot exhaust gas. The pulses of hot exhaust gases created by the combustions pass from the combustion chamber 256 through the third pipe 258 into the mixing chamber 212. The entry of the series of pulses of hot exhaust gas into the mixing chamber 212 generate a gas stream of pulsed hot exhaust gas inside of the mixing chamber 212.

The tank is filled with fluid containing the solids. The fluid containing the solids then flows into the pump 206. The pump 206 then pumps the fluid with the solids through the second pipe 208 and the nozzle 214 and into the mixing chamber 212. As the fluid with the solids passes through the nozzle 214, it is atomized into a spray 238. The spray 238 mixes with the gas stream of pulsed hot exhaust gas where it is rapidly heated, the fluid vaporising as it does so, the pulsation of the gas stream assisting the atomisation. The vaporised fluid and solids then pass out of the mixing chamber 212 through the seventh pipe 226 and into the separating chamber 230 where it is rotated rapidly to cyclonically separate the solids from the vaporised fluid. The solids then exit the separation chamber 230 through the eight solids exit pipe 232. The vaporised fluid the exits the separation chamber 230 through the ninth vapour exit pipe 234 where the vaporised fluid is condensed in the condensing chamber 272 to return it to a liquid which can then exit the condensing chamber 272 via the tenth liquid exits pipe 276. The exhaust gas can then be removed from the condensing chamber 272 via the exit fan 280 and exhaust duct 284.

A pulse combustion spray dryer has been used for extracting salts from a fluid, and as such, can be used to desalinate sea water. The paper entitled "Application of Pulse Combustion Technology in Spray Drying Process" by I Zbicinski, I Smucerowicz, C Strumillo and C Crowe of Technical University of Lodz, Faculty of Process and Environmental Engineering or Washington State University, School of Mechanical and Material Engineering, describes the use of such apparatus.

A problem with pulse combustion spray drying apparatus is that it requires the provision of a combustion fuel in order to operate. Another problem is that the fluid with the solid, once atomised are mixed with the exhaust gases of the burnt combustion fuel which may not be desirable.

The third piece of prior art is a four-stroke diesel engine will now be described in relation to Figures 3A to 30.

Referring to Figures 3A to 30, a diesel engine comprises a cylinder block 300 which is mounted on a crank shaft housing 302. The cylinder block 300 comprises an elongate cylinder 304 having a longitudinal axis and a uniform circular cross section, in a direction perpendicular to the axis, along the length of the cylinder 304. Slideably mounted within the cylinder 304 is a piston 306 of circular cross section of similar size to that of the cylinder 304. Mounted around the external sidewall of the piston 306 are piston rings (not shown) which form a seal between the external sidewall of the piston 306 and the internal side wall of the cylinder 304. The lower section of the cylinder 304 opens into a chamber 308 formed inside of the crank shaft housing 302. A rotatable crank shaft 310 is mounted inside of the crank housing 302 which is capable of rotating about an axis which extends perpendicularly to the longitudinal axis of the cylinder 304. A connecting rod 312 is pivotally attached to the crank shaft 310 at a lower end, the axis of pivot being parallel to but eccentrically off set from the axis of rotation of the crank shaft 310. The other upper end of the connecting rod 312 is pivotally attached to the piston 306, the axis of pivot being parallel to the axis of rotation of the crank shaft 310. Rotation of the crank shaft 310 results in a linear reciprocation motion of the piston 306 inside the cylinder 304 along the longitudinal axis of the cylinder 304 in well know manner. A counterweight 314 is eccentrically mounted on the crank shaft 310 to counteract any vibrations generated by the eccentric connection of the lower end of the connecting rod 312 as the crank shaft 310 rotates.

The upper section of the cylinder 304 is terminated by an upper wall formed by the top of the cylinder block 300. A combustion chamber 318 is formed inside of the upper section of the cylinder which is bounded by the upper wall of the cylinder block 300 at the top, by the inner side wall of the cylinder 304 at the sides, and the top of the piston 306 at the bottom. As the piston 306 reciprocatingly slides up and down within the cylinder 304, the volume of the chamber 318 varies, the volume of the chamber 318 being the smallest when the piston 306 is in its highest position, closest to the upper wall of cylinder block 300; the volume of the chamber 318 being the largest when the piston 306 is in its lowest position, closest to the crank shaft 310.

A first inlet passage 316 is formed through the upper wall which allows filtered air from outside of the cylinder block 300 to enter into the combustion chamber 318. A first slideable valve 320 is able to open and close the inlet passage 316. Movement of the valve 320 is controlled using a first cam shaft (not shown) in well-known manner.

A second outlet passage 326 is formed through the upper wall which allows fumes from the burnt diesel to exit from the combustion chamber 318 to outside of the cylinder block 300. A second slideable valve 322 is able to open and close the outlet passage 326. Movement of the valve 322 is controlled using a second cam shaft (not shown) in well-known manner.

An injector nozzle 324 in mounted in the upper wall between the inlet and outlet passages 316, 326 through which diesel fuel can be injected in the combustion chamber 318 in well-known manner.

Figures 3A to 3D show the combustion cycle of the engine.

Figure 3A shows the start of the cycle. At the start, the first valve 320 opens the first inlet passage 316. The second valve 322 closes the second outlet passage 326. At the star of the cycle, the piston 306 slides downwardly (Arrow A) in the cylinder 304 due to the rotation of the crank shaft 310, increasing the volume of the combustion chamber 318. As the volume of the combustion chamber 318 increases, air is drawn into the combustion chamber 318 through the first inlet passage 316.

Figure 38 shows the second stage of the combustion cycle. During the second stage, the first valve 320 closes the first inlet passage 316. The second valve 322 maintains the second outlet passage 326 closed. In the second stage, the piston 306 slides upwardly (Arrow 8) in the cylinder 304 due to the continued rotation of the crank shaft 310, decreasing the volume of the combustion chamber 318. As the volume of the combustion chamber 318 decreases, the air in the combustion chamber 318 is compressed as both the first inlet passage 316 and second outlet passage 326 are closed. As the air is compressed, its pressure and temperature in the combustion chamber 318 increases.

Figure 3C shows the third stage of the combustion cycle. During the third stage, the first valve 320 maintains the first inlet passage 316 closed. The second valve 322 also maintains the second outlet passage 326 closed. In the third stage, the piston 306 moves to its upper most position (referred to as 'top dead centre") in the cylinder 304. The volume of the combustion chamber 318 is the smallest when the piston 306 is in this position. The temperature and pressure of the air in the combustion chamber 318 are also at their highest. When the piston 306 is at top dead centre, diesel fuel is injected into the combustion chamber 318 through the nozzle 324. As the diesel fuel enters the combustion chamber 318, it begins to burn due to the elevated temperature of the air in the combustion chamber 318. The ignition of the fuel is caused by the elevated temperature of the air in the combustion chamber 318 due to the mechanical compression of the air (the diesel engine is a so-called "compression-ignition engine"). The burning of the diesel fuel causes the piston 306 to start moving downwardly (Arrow C), causing the crank shaft 310 to continue to rotate.

Figure 3D shows the end of the cycle. During the fourth stage, the first valve 320 maintains the first inlet passage 316 closed. The second outlet valve 322 opens the second outlet passage 326. During the fourth stage, the piston 306 slides upwardly (Arrow D) in the cylinder 304 due to the rotation of the crank shaft 310, decreasing the volume of the combustion chamber 318. As the volume of the combustion chamber 318 decreases, the fumes generated by the burning of the diesel fuel in the air in the combustion chamber 318 is expelled from the combustion chamber 318 through the second outlet passage 326.

Diesel engines work by compressing only the air (not a mixture of air and diesel fuel). A typical compression ratio of a diesel engine is between 14 to 1 and 22 to 1. This increases the air temperature inside the combustion chamber 318 to such a high degree that when atomised diesel fuel is injected into the combustion chamber 318, it ignites spontaneously. The temperature inside of the combustion chamber 318 when the air is fully compressed is typically greater than 526 degrees Centigrade (>979 degrees Fahrenheit).

It will be appreciated that there are also two stroke diesel engines. These also ignite atomised diesel fuel by first compressing the air inside of a combustion chamber to increase the temperature of the compressed air and then secondly injecting the diesel fuel into the combustion chamber to be ignited by the high temperature of the compressed air.

Accordingly, there is provided a piston compressor for a pulse spray dryer in accordance with claim 1.

It will be appreciated that the cylinder block can be form in a one-piece construction or can be constructed from a number of component parts attached to each other.

Whilst it is desirable to use a single piston in the construction of the piston compressor to minimise the number of component parts, it is possible to construct a piston compressor using a plurality of pistons. For example, the piston compressor could comprise two pistons slideably mounted within the cylinder adjacent each other, each of which are reciprocating driven within the cylinder, the compression chamber being formed by the ends of the two pistons which are facing each other within the cylinder and the internal walls of the cylinder.

Preferably, the at least one valve allows the gas to exit the compression chamber when the gas has been compressed and the pressure and temperature of the gas has been increased in the form of a pulse.

Ideally, there is only one piston located within the cylinder.

There may be at least one outlet through which gas can exit the compression chamber. If so, ideally, the at least one valve is connected to the at least one outlet. The outlet may be is a passageway formed through the cylinder block which is capable of connecting to the compression chamber. It will be appreciated that the outlet passageway may either be connected to the compression chamber all of the time or is only connected to the compression chamber during certain parts of the operating cycle of the piston compressor.

Ideally, there is at least one inlet through which gas can enter the compression chamber. The at least one valve can be connected to the at least one inlet. The inlet can be a passageway formed through the cylinder block which is capable of connecting to the compression chamber. It will be appreciated that the inlet passageway may either be connected to the compression chamber all of the time or may only be connected to the compression chamber during certain parts of the operating cycle of the piston compressor.

When the reciprocating drive mechanism is reciprocatingly driving the at least one piston within the cylinder to change the volume the of the compression chamber of the piston compressor, the least one timing device can operate the at least one valve to enable the at least one valve to allow the gas to enter the compression chamber when the volume of the compression chamber is increasing or when the volume of the compression chamber is at its maximum.

When the reciprocating drive mechanism is reciprocatingly driving the at least one piston within the cylinder to change the volume the of the compression chamber of the piston compressor, the least one timing device can operates the at least one valve to enable the at least one valve to allow the gas to exit the compression chamber when the volume of the compression chamber is decreasing or when the volume of the compression chamber is at its minimum and the pressure and temperature of the gas has been increased.

When the reciprocating drive mechanism is reciprocatingly driving the at least one piston within the cylinder to change the volume the of the compression chamber of the piston compressor, the least one timing device can operate the at least one valve to enable the at least one valve to allow the gas to exit the compression chamber when the pressure and temperature of the gas has been increased.

Preferably, the pressure of the gas when it enters the compression chamber is substantially less than when it exits the compression chamber. Preferably, the temperature of the gas when it enters the compression chamber is substantially less than when it exits the compression chamber.

The at least one valve can be capable of connecting to a pulse spray dryer so that, when the gas exits the compression chamber, it enters the pulse spray dryer.

Preferably, the at least one timing device comprises the at least one valve.

The at least one timing device may open and closes the at least one valve dependent on the direction of movement of the at least one piston within the cylinder. If so, preferably the at least one timing device can open the at least one valve when the at least one piston is sliding within the cylinder to increase the volume of the compression chamber and the at least one timing device closes the at least one valve when the at least one piston is sliding within the cylinder to decrease the volume of the compression chamber.

Alternatively or in addition, the at least one timing device can open and close the at least one valve dependent on the position of the piston within the cylinder. If so, preferably the at least one timing device opens the at least one valve at least when the at least one piston is located within the cylinder when the volume of the compression chamber is at its minimum.

The at least one valve is a purely a mechanical valve. Alternatively, the at least one valve is an electronically controlled valve. If so, the at least one valve may be a three way electronically controlled valve.

There may be two valves, a first valve which enables gas to enter the compression chamber and a second valve which enables the gas to exit the compression chamber. If so, the first valve can enable the gas to enter the compression chamber when the movement of the at least one piston in the cylinder results in an increase the volume of the compression chamber. Also, the second valve can enable the gas to exit the compression chamber when the position of the at least one piston in the cylinder is such that the volume of the compression chamber is at its minimum. The second valve can also be capable of connecting the compression chamber to a pulse spray dryer so that, when the gas exits the compression chamber, it is capable of entering the pulse spray dryer.

The at least one timing device may open and close the at least one valve.

The reciprocating drive mechanism may be connected to the at least piston via the at least one valve.

Where the at least one valve is a mechanical valve, it can be mounted within the at least one piston and comprises a valve chamber formed in the at least one piston; a tubular passage which extends from the valve chamber through the at least one piston to the compression chamber; a second upper elongate tubular passage which extends from the valve chamber through the at least one piston to the upper surface of the at least one piston and which is capable of allowing gas to freely pass between the valve chamber and a space above the piston; at least one valve disk moveably mounted within the valve chamber and moveable between a first position and a second position, wherein when the at least one valve disk is in its first position, it seals the tubular passage to prevent gas from passing through it and when the at least one valve disk is in its second position, it opens the tubular passage to allow gas to pass through it; a slide rod connected to the at least one valve disk, movement of the slide rod moving the at least one valve disk between its two positions.

It will be appreciated that the slide rod can be moved using many different mechanisms, whether mechanical or electrical. If such mechanisms are located externally of the piston, then the slide rod will need to extend from the valve chamber to the outside of the piston. The slide rod could extend from valve chamber through either the tubular passage or the second upper elongate tubular passage. Alternatively, the slide rod could extend through another separate tubular passage.

The at least one valve can further provide another first upper tubular passage which extends from the valve chamber through the at least one piston to the upper surface of the at least one piston, wherein the first upper elongate passage extends parallel to and is co-axial with the longitudinal axis of the cylinder; wherein the second upper elongate passage extends parallel to but is offset from the longitudinal axis of the cylinder; wherein the slide rod is slidably mounted inside of a side bearing mounted within the first upper tubular passage.

The slide rod may extend parallel to and is co-axial with the longitudinal axis of the cylinder and is capable of sliding axially along its longitudinal axis within the slide bearing. The upper end of the slide rod can be pivotally attached to the lower end of a connecting rod of the reciprocating drive mechanism.

A biasing mechanism can be sandwiched between a wall of the valve chamber and the at least one valve disk, the biasing mechanism biasing the at least one valves disk towards its first position.

A seal may be mounted on the at least one valve disk wherein when the at least one valve disk is in its first position, the seal is sandwiched between the at least one valve disk and a side wall of the valve chamber to seal the entrance to the lower elongate tubular passage.

The reciprocating drive mechanism may comprise a crank shaft connected to the slide rod; wherein, when the crank shaft rotates to slide the at least one piston inside of the cylinder, the crank shaft first causes the slide rod to slide inside the slide bearing to move the at least one valve disk inside of the valve chamber between its two positions, before it causes the at least one piston to slide within the cylinder.

In addition or alternatively, the at least one valve of the piston compressor may be a mechanical valve which comprises: an outlet formed through the wall of the cylinder which faces towards the side of the at least one piston; at least one seal sandwiched between the side of the at one piston and the wall of the cylinder and which prevents gas from passing to or from, above or below, the at least one piston, between the side of the at least one piston and the wall of the cylinder and enter or exit the outlet; a U-shaped passage formed through the at least one piston having a lower entrance at one end of the U shaped passage formed in the side wall of the at least one piston and an upper entrance at the other end of the U shaped passage formed in the side wall of the at least one piston and which is located axially above the lower entrance; wherein, when the at least one piston reciprocatingly slides up and down within the cylinder, the U-shaped passage is capable of enabling gas to pass around the at least one seal and allow gas to pass to or from, above or below, the at least one piston, and enter or exit the outlet; wherein, during certain parts of the operating cycle, gas is able to exit the compression chamber, pass between the side of the piston, pass around the at least one seal by entering one of entrances of the U shaped passage, pass through the U shaped passage and exit the other entrance of the U shaped passage, and then enter the outlet.

There can be two seals, each formed around the circumference of the inner wall of the cylinder, adjacent to each other in axial direction of the cylinder; wherein the outlet is formed between the two seals; wherein, during certain parts of the operating cycle, one of the entrances of the U shaped passage connects to the space between the seals whilst the other entrance of the U shaped passage connects to a space to one side of the two seals.

According to another aspect of the present invention there is provided a piston compression pulse spray dryer comprising at least one piston compressor as described above and below, and at least one pulse spray dryer; wherein the at least one piston compressor provides a series of pulses of compressed heated gas to the at least one pulse spray dryer.

Pulse combustion spray dryers are well known in the art and comprise a pulse combustor, which produces a series of pulses of heated exhaust gases, and a pulse spray dryer. It will be appreciated that a piston compression pulse spray dryer according to present invention can comprise a piston compressor, as described herein and covered by the claims, with any known design of pulse spray dryer of an existing pulse combustion spray dryer.

It will be appreciated a plurality of piston compressors could provide series of pulses of compressed heated gas to a single pulse spray dryer, or a single piston compressor could provide a series of pulses of compressed heated gas to a plurality of pulse spray dryers or a plurality of piston compressors could provide series of pulses of compressed heated gas to a plurality of pulse spray dryers.

The at least one pulse spray dryer may comprise: a tank for a substance to be separated fluid containing the solids; a housing which forms a mixing chamber; a supply passage which connects the tank to the mixing chamber; a separator which forms a separation chamber which comprises a first exit and a second exit; a separator passage which connects the mixing chamber to the separation chamber; wherein the at least one piston compressor is connected to the mixing chamber and is capable of providing a series of pulses of compressed heated gas to the mixing chamber; wherein the tank is capable of providing the fluid with solids to the mixing chamber via the supply passage; wherein, when the at least one piston compressor provides a series of pulses of compressed heated gas to the mixing chamber and the tank provides fluid with solids to the mixing chamber, the pulses of compressed heated gas mix with the fluid with solids in the mixing chamber to form a mixture of vapourised fluid and solids; wherein the mixture of vapourised fluid and solids exits the mixing chamber and enters the separator via the separator passage where the vapourised fluid is separated from the solids; wherein the solids exit the first exit and the vapourised fluid exits the second exit.

Whilst the embodiments of the piston compression pulse spray dryer are described in relation to separating solids for a fluid, It will be appreciated that such a piston compression pulse spray dryer can be used to separate fluids from fluids, solids from solids or multiple types of combinations of substances.

The fluid with the solids can pass through a nozzle as it enters the mixing chamber to atomise the fluid. The fluid containing the solids can flow into the mixing chamber due to gravity.

However, it is preferable that the flow is assisted. However, it may be preferable to provide a pump to assist with the flow of the fluid containing the solids into the mixing chamber.

A lower portion of the housing which forms the mixing chamber also forms the separator. The separator may be a cyclonic separator. The separator may form a separation chamber which tapers at its lower end to the first exit. The second exit may comprise a vapour pump to assist in the removal of the vapourised fluid from the separator. The vapourised fluid can also pass through a condenser as it leaves through the second exit in order to be condensed back into a fluid. Furthermore, there can be provided a collection tank to collect the condensed fluid.

Ideally, the combined volumes of the compression chamber at Its smallest volume V2 and the volume V3 of the interconnection passageway between the compression chamber and the mixing chamber is less than the volume of the compression chamber at its maximum volume V1, and ideally significantly less. Preferably, the volume of V2 + V3 is less than 95% of V1, and preferably, the volume of V2 + V3 is less than 90% of V1, and more preferably, the volume of V2 + V3 is less than 50% of V1, and more preferably, the volume of V2 + V3 is less than 30% of VI. the volume of V2 + V3 is less than 10% of Vi.

Ideally, the combined volumes of the compression chamber at its smallest volume V2, the volume V3 of the interconnection passageway between the compression chamber and the mixing chamber and the volume V4 of the mixing chamber needs to be less than the volume of the compression chamber at its maximum volume V1, and ideally significantly less. Preferably, the volume of V2 + V3 + V4 is less than 95% of V1, and preferably, the volume of V2 + V3 + V4 is less than 90% of V1, and more preferably, the volume of V2 + V3 + V4 is less than 50% of V1, and more preferably, the volume of V2 + V3 + V4 is less than 30% of V1 the volume of V2 + V3 + V4 is less than 10% of Vi.

According to another aspect of the present invention there is provided a method of desalinating a salt solution using a piston compression pulse spray dryer as described above and below wherein the method comprises the steps of: placing water with a salt dissolved within it as the fluid with the solids in the tank; operating the piston compression pulse spray dryer so that the salt exits the first exit and water exits the second exit. The water with the salt dissolved within it can be sea water.

Relevant prior art (described above) and three embodiments of the invention (described below) will now be described with reference to the following drawings of which: Figure 1 shows a prior art design of spray drying apparatus; Figure 2 shows a prior art design of pulse combustion spray dryer; Figure 3A shows a vertical cross section of a prior art four-stroke diesel engine when the piston is moving downwardly (Arrow A) within the cylinder to draw air into the combustion chamber of the cylinder; Figure 3B shows a vertical cross section of the four-stroke diesel engine of Figure 3A when the piston is moving upwardly (Arrow B) within the cylinder to compress the air within the combustion chamber of the cylinder; Figure 3C shows a vertical cross section of the four-stroke diesel engine of Figure 3A when the piston is at top dead centre within the cylinder before moving downwardly (Arrow C) within the cylinder after the ignition of diesel fuel and air in the combustion chamber of the cylinder; Figure 30 shows a vertical cross section of the four-stroke diesel engine of Figure 3A when the piston is moving upwardly (Arrow Co) within the cylinder to expel burnt diesel fuel and air from the combustion chamber of the cylinder; Figure 4A shows a vertical cross section of a piston compression pulse spray dryer according to a first embodiment of the present invention when the piston is at its highest position with the compression chamber at its largest volume filled with air at atmospheric pressure; Figure 48 shows a vertical cross section of a piston compression pulse spray dryer of Figure 4A when the piston is moving downwardly (Arrow N), reducing the volume of the compression chamber to compress and heat the air within the compression chamber; Figure 4C shows a vertical cross section of a piston compression pulse spray dryer of Figure 4A when the piston is at its lowest position and the volume of the compression chamber at its smallest with the air within the compression chamber fully compressed and heated; Figure 40 shows a vertical cross section of a piston compression pulse spray dryer of Figure 4A when the piston is moving upwardly (Arrow 0), increasing the volume of the compression chamber whilst it is being filled with air at atmospheric pressure; Figure 5 shows a vertical cross section of a piston compression pulse spray dryer according to a second embodiment of the present invention which comprises four piston compressors; Figure 6A shows a vertical cross section of a piston compressor of a piston compression pulse spray dryer according to a third embodiment of the present invention which comprises two electronically controlled valves; Figure 6B shows the status of the two valves in comparison with the volume of the compression chamber; Figure 7A shows a vertical cross section of a piston compression pulse spray dryer according to a fourth embodiment of the present invention which comprises a single three way electronically controlled valve; and Figure 7B shows the status of the three way electronically controlled valve in comparison with the volume of the compression chamber.

The first embodiment of the invention will now be described with reference to Figures 4A to 4D.

Referring to Figures 4A to 40, a piston compression pulse spray dryer comprises a piston compressor 484 which produces a series of pulses of compressed hot air and a pulse spray dryer 490.

The piston compressor 484 comprises a cylinder block 400 which is mounted below a crank shaft housing (not shown). The cylinder block 400 comprises an elongate cylinder 404 having a longitudinal axis and a uniform circular cross section, in a direction perpendicular to the axis, along the length of the cylinder 404. Slideably mounted within the cylinder 404 is a piston 406 of circular cross section of similar size to that of the cylinder 404. Mounted circumferentially around the internal wall of the cylinder 404 towards the top of the cylinder 404 are two seals 408 which form a seal between the external sidewall of the piston 406 and the inner side wall of the cylinder 404 and which prevent any gases from passing the seals 408. The seals 408 slide along the external sidewall of the piston 406 when the piston 406 reciprocates within the cylinder 404. The upper section of the cylinder 404 opens into a chamber 410 formed inside of the crank shaft housing. The lower section of cylinder 404 forms a compression chamber 428, the compression chamber 428 being defined by the lower internal walls of the cylinder 404 and a lower surface 417 of the piston 406.

A rotatable crank shaft 412 is mounted inside of the crank shaft housing which is capable of rotating about an axis which extends perpendicularly to the longitudinal axis of the cylinder 404. A connecting rod 414 is pivotally attached to the crank shaft 412 at an upper end, the axis of pivot being parallel to but eccentrically off set from the axis of rotation of the crank shaft 412. The lower end of the connecting rod 414 is pivotally attached to a first valve 416 formed in the top of the piston 406, the axis of pivot being parallel to the axis of rotation of the crank shaft 412. Rotation of the crank shaft 412 results in a linear reciprocation motion of the piston 406 inside the cylinder 404 along the longitudinal axis of the cylinder 404 in well known manner. A counterweight (not shown) is eccentrically mounted on the crank shaft 412 to counteract any vibrations generated by the eccentric connection of the upper end of the connecting rod 414 as the crank shaft 412 rotates.

The first valve 416 comprises a valve chamber 418 formed in the top of the piston 406. The valve chamber 418 is circular in cross-section (perpendicularly to the longitudinal axis of the cylinder 404) with a flat lower side wall 420 and a flat upper side wall 422. A lower elongate tubular passage 424 extends from the lower side wall of the valve chamber 418 through the piston 406 to the lower surface 417 of the piston 406. The lower elongate tubular passage 424 allows air to freely pass between the valve chamber 418 and the compression chamber 428 of the cylinder 404.

A first upper elongate tubular passage 434 extends from the upper side wall 422 of the valve chamber 418 through the piston 406 to the upper surface of the piston 406. The first upper elongate passage 434 extends parallel to and is co-axial with the longitudinal axis of the cylinder 404.

A second upper elongate tubular passage 436 extends from the upper side wall 422 of the valve chamber 418 through the piston 406 to the upper surface of the piston 406. The second upper elongate passage 436 extends parallel to and but is offset from the longitudinal axis of the cylinder 404. The second upper elongate tubular passage 436 allows air to freely pass between the valve chamber 418 and the space 410 above the piston 406 facing towards and/or connected to the chamber in the crank shaft housing.

Mounted inside of the valve chamber 418 are two valve disks 430, 432. The top disk 430 is mounted on top of the lower disk 432, the two disks 430 432 being integrally formed as one component. The valve disks 430, 432, are circular in cross-section (perpendicularly to the longitudinal axis of the cylinder 404), both having the same constant thickness (parallel to the longitudinal axis of the cylinder 404), both being smaller in diameter that the valve chamber 418, the top disk 430 being smaller In diameter than the lower disk 432.

The top disk 430 is rigidly attached to the lower end of a slide rod 438. The slide rod 438 is sldieably mounted inside of a side bearing 440 mounted within the first upper tubular passage 434. The slide rod 438 extends parallel to and is co-axial with the longitudinal axis of the cylinder 404 and is capable of sliding axially along its longitudinal axis within the slide bearing 440. The upper end of the slide rod 438 is pivotally attached to the lower end of the connecting rod 414, the axis of pivot being parallel to the axis of rotation of the crank shaft 412. Rotation of the crank shaft 412 results in a linear reciprocation motion of the slide rod 438 inside of the slide bearing 440.

A weak helical spring 442 is sandwiched between the upper side wall 422 of the valve chamber 418 and top surface of the disk 432, the lower end of the spring 442 surrounding the top disk 430. The spring 442 biases the two valves disks 430,432 towards their lowest position in the valve chamber 418.

A seal 444 is mounted on the lower surface of the lower disk 432. When the two valve disks 430, 432 are in their lowest position (as shown in Figures 4B and 4C), the seal 444 is sandwiched between the lower surface of the lower disk 432 and the lower flat side wall 420 of the valve chamber 418. When the seal 444 and valve disks 430, 432 are in this position, the entrance to the lower elongate tubular passage 424 is sealed, thus preventing air from passing between the valve chamber 418 and the compression chamber 428 of the cylinder 404. When the two valve disks 430, 432 are in their highest position (as shown in Figures 4A and 4D), the seal 444 is located away from the lower flat side wall 420 of the valve chamber 418. When the seal 444 and valve disks 430, 432 are in this position, the entrance to the lower elongate tubular passage 424 is open, thus allowing air to pass freely between the valve chamber 418 and the compression chamber 428 of the cylinder 404.

When the crank shaft 412 rotates to move the piston 406 downwardly inside of the cylinder 404, the crank shaft 412, causes the slide rod 438 to slide downwardly inside the slide bearing 440, moving the two valve disks 430, 432 downwardly inside of the valve chamber 418 until the two valve disks 430, 432 are in their lowest position (as shown in Figures 48 and 4C) with the seal 444 sandwiched between the lower surface of the lower disk 432 and the lower flat side wall 420 of the valve chamber 418. As the crank shaft 412 continues to rotate to move the piston 406 downwardly inside of the cylinder 404, the crank shaft 412, continues to push the slide rod 438 downwardly, the slide rod 438 pushing the valve disks 430, 432 downwardly, which in turn push the piston 406 downwardly inside of the cylinder 404 by their engagement of the lower wall 420 of the valve chamber 418. As the valve 430, 432 pushes the piston 406 downwardly, the entrance to the lower elongate tubular passage 424 is sealed, thus preventing air from passing between the valve chamber 418 and the compression chamber 428 of the cylinder 404 as the piston 406 moves downwardly within the cylinder 404.

When the crank shaft 412 rotates to move the piston 406 upwardly inside of the cylinder 404, the crank shaft 412 causes the slide rod 438 to slide upwardly inside the slide bearing 440, moving the two valve disks 430,432 upwardly inside of the valve chamber 418 until the two valve disks 430, 432 are in their highest position (as shown in Figures 4A and 40) with the seal 444 located remotely from flat lower wall 420 of the valve chamber 418 and the upper disk 430 located against the upper flat side wall 422 of the valve chamber 418. As the crank shaft 412 continues to rotate to move the piston 406 upwardly inside of the cylinder 404, the crank shaft 412, continues to pull the slide rod 438 upwardly, the slide rod 438 pulling the valve disks 430, 432 upwardly, which in turn pull the piston 406 upwardly inside of the cylinder 404 by their engagement of the flat upper side wall 422 of the valve chamber 418. As the valve 430, 432 pulls the piston 406 upwardly, the entrance to the lower elongate tubular passage 424 is open, thus allowing air to pass between the valve chamber 418 and the compression chamber 428 of the cylinder 404 as the piston 406 moves upwardly within the cylinder 404.

The design of the first valve 416 is such that it acts a timing device for the entry of air into the compression chamber 428. When the piston 406 is moving upwardly, the first valve 416 opens, allowing air to enter into the compression chamber 428. When the piston 406 is moving downwardly, the first valve 416 closes, preventing air entering or exiting the compression chamber 428. A such, the first valve 416 controls when and when not air can pass through the first valve 416 dependent on the direction of movement of the piston 406 by the crank shaft 412.

The lower section of the cylinder 404 is terminated by a lower wail formed by the bottom of the cylinder block 400. The compression chamber 428 is formed inside of the lower section of the cylinder 404 which is bounded by the lower wall of the cylinder block 400 at the bottom, by the side wall of the cylinder 404 at the sides, and the lower surface 417 of the piston 406 at the top. As the piston 406 reciprocatingly slides up and down within the cylinder 404, the volume of the compression chamber 428 varies, the volume of the compression chamber 428 being the smallest when the piston 406 is in its lowest position as shown in Figure 4C, closest to the lower inner wall of cylinder block 400, the volume of the chamber 428 being the largest when the piston 406 is in its highest position, closest to the crank shaft 412, as shown in Figure 4A.

An outlet 446 is formed through the wall of the cylinder 404. The outlet 446 is located between the two seals 408. Formed in the side of the piston 406 is a U-shaped passage 448. The U shaped passage 448 and the two seals 408 form a second valve 486. The U shaped passage 448 connects between a lower entrance 450 formed in the side wall of the piston 406 and an upper entrance 452 formed inside wall of the piston 406 and which is located axially above the lower entrance 450. When the piston 406 reciprocatingly slides up and down, the U-shaped passage 448 similarly slides up and down with it. When the piston 406 is at its lowest position as shown in Figure 4C, the lower entrance 450 of the U shaped passage 448 is located below the lower of the two seals 408 whilst the upper entrance 452 of the U shaped passage 448 faces into the space formed between the two seals 408 towards the outlet 446. When the piston 406 is in this position, the air in the compression chamber 428, which is compressed and heated due to the compression chamber 428 having its smallest volume, is able to pass between the side of the piston 406, enter the lower entrance 450 of the U shaped passage 448, pass through the U shaped passage 448 and exit the upper entrance 452 of the U shaped passage 448, enter the space between the two seals 408 and then enter the outlet 446. The U shaped passage 448 enables the compressed heated air to by-pass the lower of the two seals 408, thus allowing the compressed heated air from the compression chamber 428 to exit via the outlet 446 when the piston 406 is located in this position.

When the piston starts to move upwardly from its lowest position shown in Figure 4C, for a brief period of time, the upper entrance 452 of the U shaped passage 448 is located above the upper of the two seals 408 whilst the lower entrance 450 of the U shaped passage 448 faces into the space formed between the two seals 408 towards the outlet 446. During the brief period when the piston 406 is in this position, air located above the piston 406 is able to pass between the side of the piston 406 and the cylinder wall, enter the upper entrance 452 of the U shaped passage 448, pass through the U shaped passage 448, exit the lower entrance 450 of the U shaped passage 448, enter the space between the two seals 408 and then enter the outlet 446.

Similarly, when the piston 406 is moving downwardly and is approaching its lowest position as shown in Figure 4C, for a brief period of time, the upper entrance 452 of the U shaped passage 448 is located above the upper of the two seals 408 whilst the lower entrance 450 of the U shaped passage 448 faces into the space formed between the two seals 408 towards the outlet 446. During the brief period when the piston 406 is in this position, air located above the piston 406 is able to pass between the side of the piston 406 and the cylinder wall, enter the upper entrance 452 of the U shaped passage 448, pass through the U shaped passage 448, exit the lower entrance 450 of the U shaped passage 448, enter the space between the two seals 408 and then enter the outlet 446.

During the rest of the cycle of the reciprocation of the piston 406, both of the entrances 450, 452 are located above both seals 408. As such, the space between the seals 408 is sealed by the side of the piston 406, sealing the entrance to outlet 446. As such, air is unable to pass through the outlet 446.

The design of the second valve 486 is such that it acts a timing device for the exit of air from the compression chamber 428. When the piston 406 has moved to its lowest position, the second valve 486 opens, allowing air to exit the compression chamber 428. When the piston 406 subsequently moves upwardly, the second valve 486 closes, preventing air entering or exiting the compression chamber 428 through the second valve 486. As such, the second valve 486 controls when and when not air can pass through the second valve 486 dependent on the position of the piston 406 within the cylinder 404.

The pulse spray dryer 490 comprises a tank 454 in which is inserted the fluid 456 containing the solids. A first pipe 462 connects the tank 454 to a housing 458 which forms a mixing chamber 460 in its upper portion. The first pipe 462 passes through the wall of the housing 458 and extends into the mixing chamber 460. A nozzle 464 is attached to the end of the first pipe 462 inside of the mixing chamber 460. The fluid 456 containing the solids can flow into the mixing chamber 460 due to gravity.

However, it will be appreciated that a pump (not shown) can be used to assist with the flow of the fluid 456 containing the solids into the mixing chamber 460, the pump pumping the fluid 456 containing the solids into the mixing chamber 460 under a higher pressure than that generated by gravity.

Attached to the top of the housing 458 is a second pipe 466 which connects between the outlet 446 and the housing 458.

The lower portion of the housing 458 forms a cyclonic separator 468. The cyclonic separator 468 forms a separation chamber 470 which tapers at its lower end to a third solids exit pipe 472.

A fourth vapour exit pipe 474 connects to an aperture formed through an upper part of the wall of the cyclonic separator 468 to a vapour pump 476. The fourth vapour exit pipe 474 is made of material, such as metal, which conducts heat efficiently. Attached, in a heat conductive manner, to the side of the fourth vapour exit pipe 474, are a series of fins 478, each of which are made from heat conductive material such as metal. The fourth vapour exit pipe 474, together with the fins 478, act as a condenser, cooling any gases, liquids and/or and vapours which pass through the fourth vapour exit pipe 474 from the cyclonic separator 468 to the vapour pump 476.

A fifth exit pipe 480 connects to the vapour pump 476 and extends downwardly towards a collection tank 482.

The operation of the piston compression pulse spray dryer will now be described with reference to Figures 4A to 4D. During the operation of the piston compression pulse spray dryer, the piston compressor 484 produces a series of pulses of compressed hot air. These are fed into the pulse spray dryer 490 where the pulses of compressed hot air are mixed with the atomised fluid 456 containing the solids. The pulses of compressed hot air cause the fluid 456, containing the solids to vaporise, liberating the solids from the fluid 456. The solids are then separated from the vaporized fluid 456 and then discharged from the pulse spray dryer 490. The vaporized fluid is then condensed, discharged from the pulse spray dryer 490 and then collected.

Figures 4A to 4D show the operating cycle of the piston compression pulse spray dryer, Figures 4A to 4D showing the piston compressor 484 in four different operating positions during the cycle.

In order for the piston compressor 484 to operate to produce a series of pulses of compressed hot air, the crank shaft 412 of the pulse compressor must be rotationally driven (Arrow M) by an external rotary force.

The crank shaft 412 is rotationally driven in the direction of Arrow M in order drive the piston compressor 484 through its cycle. The crank shaft 412 is rotated using the external force. Such a force can be generated by a separate fan or propellor (not shown) due to the movement of air or water through the fan or propellor such as wind acting on a wind turbine or sea water passing through a water turbine due to the movement of the water caused by the tide. Alternatively, the force could be generated by an electric motor (not shown), a pneumatic motor (not shown), a hydraulic motor (not shown), a petrol or diesel engine (not shown) or any known device which is capable of generating a rotational movement.

Figure 4A shows the start of the cycle. At the start, the crank shaft 412 has moved the piston 406, using the connecting rod 414, to its highest position within the cylinder 404. The connecting rod 414 is attached to the slide rod 438 of the first valve 416. Because the crank shaft 412 has moved the piston 406 to its highest position, the slide rod 438 has been slid upwardly inside the slide bearing 440, moving the two valve disks 430, 432 upwardly inside of the valve chamber 418 until the two valve disks 430, 432 are in their highest position (as shown in Figures 4A) with the seal 444 located remotely from lower wall 420 of the valve chamber 418 and the upper disk 430 located against the upper wall of the valve chamber 418. As such, the entrance to the lower elongate tubular passage 424 is open, thus allowing air to pass between the valve chamber 418 and the compression chamber 428 of the cylinder 404. The compression chamber 428 is at its greatest volume Vi when the piston 406 is in its highest position. As the valve disks 430, 432 are in their highest position, air is able pass from above the piston 406 from the surrounding atmosphere, through the second upper elongate passage 436, through the valve chamber 418 and then through the lower elongate tubular passage 424 and into the compression chamber 428 of the cylinder 404. As such, the air pressure inside the compression chamber 428 is the same as that of the atmosphere surrounding the piston compression pulse spray dryer.

When the piston 406 is in its highest position, as shown in Figure 4A, both of the entrances 450, 452 of the U shaped passage 448 of the second valve 486, are located above both seals 408. As such, the space between the seals 408 is sealed by the side of the piston 406 and therefore the entrance to outlet 446 is sealed by the second valve 486 and as such, air is unable to pass through the outlet 446.

Figure 4B shows the second stage of the cycle. During the second stage, the crank shaft 412 is moving the piston 406 downwardly (Arrow N), using the connecting rod 414 which is attached to the first valve 416.

As the crank shaft 412 rotates (Arrow M) to move the piston 406 downwardly inside of the cylinder 404, the crank shaft 412 causes the slide rod 438 to slide downwardly inside the slide bearing 440, moving the two valve disks 430, 432 downwardly inside of the valve chamber 418 until the two valve disks 430, 432 are in their lowest position (as shown in Figure 4B) with the seal 444 sandwiched between the lower surface of the lower disk 432 and the flat side wall 420 of the valve chamber 418. As the crank shaft 412 continues to rotate (Arrow M) to move the piston 406 downwardly inside of the cylinder 404, the crank shaft 412 continues to push the slide rod 438 downwardly, the slide rod 438 pushing the valve disks 430,432 downwardly, which in turn push the piston 406 downwardly inside of the cylinder 404 by their engagement of the lower wall 420 of the valve chamber 418. As the valve 430, 432 pushes the piston 406 downwardly (Arrow N), the entrance to the lower elongate tubular passage 424 is sealed, thus preventing air from passing between the valve chamber 418 and the compression chamber 428 of the cylinder 404 as the piston 406 moves downwardly within the cylinder 404. As such, air is unable to pass from above the piston 406 from the surrounding atmosphere into the compression chamber 428 of the cylinder 404.

When the piston is being moved downwardly (Arrow N) by the crank shaft 412 as shown in Figure 413, both of the entrances 450, 452 of the U shaped passage 448 of the second valve 486, remain located above both seals 408. As such, the space between the seals 408 is sealed by the side of the piston 406 and therefore the entrance to outlet 446 is sealed by the second valve 486 and as such, air is unable to pass through the outlet 446.

As such, the compression chamber 428 in the cylinder 404 is completely sealed, with air being unable exit through either the first or second valves 416, 486. Therefore, as the piston 406 moves downwardly, the air located in the compression chamber 428 becomes compressed, with both the pressure and temperature of the air within the compression chamber 428 increasing. As the air pressure in the compression chamber increases, an upward force is exerted onto the piston 406, which in turn assists in maintaining the engagement of the disks 430, 432 and seal 444 with the lower wall 420 of the valve chamber 418.

Figure 4C shows the third stage of the cycle. During the third stage, the crank shaft 412 has moved the piston 406 to its lowest position within the cylinder 404. In this position, the compression chamber 428 has its smallest volume V2. As such, the air located in the compression chamber 428 is at its maximum compression with both the pressure and temperature of the air in the compression chamber 428 being at their maximum. As the air pressure in the compression chamber is much higher than that exerted on the top of the piston 406 (which is that of the surrounding atmosphere), an upward force is exerted onto the piston 406. As such, the two valve disks 430, 432 are maintained in their lowest position in the valve chamber 418 (as shown in Figure 4C) with the seal 444 is sandwiched between the lower surface of the lower disk 432 and the flat side wall 420 of the valve chamber 418. Therefore, the entrance to the lower elongate tubular passage 424 remains sealed, thus preventing air from passing between the valve chamber 418 and the compression chamber 428 of the cylinder 404.

As the piston 406 moves downwardly (Arrow N), towards the position shown in Figure 4C, for a brief period of time, the upper entrance 452 of the U shaped passage 448 is located above the upper of the two seals 408 whilst the lower entrance 450 of the U shaped passage 448 faces into the space formed between the two seals 408 towards the outlet 446. During the brief period when the piston 406 is in this position, air located above the piston 406 is able to pass between the side of the piston 406 near the top of the piston 406 and the cylinder wall, enter the upper entrance 452 of the U shaped passage 448, pass through the U shaped passage 448 and exit the lower entrance 450 of the U shaped passage 448, enter the space between the two seals 408 and then enter outlet 446.

When the piston has moved to its lowest position as shown in Figure 4C, the lower entrance 450 of the U shaped passage 448 is located below the lower of the two seals 408 whilst the upper entrance 452 of the U shaped passage 448 faces into the space formed between the two seals 408 towards the outlet 446. When the piston 406 is in this position, the air in the compression chamber 428, which is at its maximum compression and highest temperature due to the compression chamber having its smallest volume V2, is able to pass between the lower side of the piston 406, enter the lower entrance 450 of the U shaped passage 448, pass through the U shaped passage 448 and exit the entrance 452 of the U shaped passage 448, enter the space between the two seals 408 and then enter the outlet 446. As the air in the compression chamber 428 is at its maximum pressure and temperature, a pulse of compressed and heated air enters the outlet 446. The pulse of compressed and heated air then passes through the second pipe 466 and into the mixing chamber 460 of the housing 458 of the pulse spray dryer 490.

As the pulse of compressed and heated air passes between the side of the piston 406, enters the lower entrance 450 of the U shaped passage 448, passes through the U shaped passage 448 and exits the upper entrance 452 of the U shaped passage 448, enters the space between the two seals 408, enters the outlet 446, through the second pipe 466 and into the mixing chamber 460 of the housing 458, the pressure and temperature of the pulse of air will drop as the air expands and cools. As such, the combined volumes of the compression chamber at its smallest volume V2 (Figure 4C) and the volume V3 of the interconnection passageway between the compression chamber 428 and the mixing chamber 460 (comprising the volume of the space down the lower side of the piston 406, the volume of the space in the U shaped passage 448, the volume of space between the two seals 408 and the volume within the second pipe 466) needs to be less than the volume of the compression chamber 428 at its maximum volume V1, and ideally significantly less, in order to ensure that the pulse of air entering the mixing chamber 460 is at a reasonable pressure and temperature in order for it to vaporise any atomised fluid entering the mixing chamber 460. Ideally, the volume of V2 + V3 is less than 95% of V1, and preferably, the volume of V2 + V3 is less than 90% of V1, and more preferably, the volume of V2 + V3 is less than 50% of V1, and more preferably, the volume of V2 + V3 is less than 30% of V1 the volume of V2 + V3 is less than 10% of Vi.

Ideally, the combined volumes of the compression chamber 428 at its smallest volume V2 (Figure 4C), the volume V3 of the interconnection passageway between the compression chamber 428 and the mixing chamber 460 (comprising the volume of the space down the lower side of the piston 406, the volume of the space in the U shaped passage 448, the volume of space between the two seals 408 and the volume within the second pipe 466) and the volume V4 of the mixing chamber 460 needs to be less than the volume of the compression chamber 428 at its maximum volume V1, and ideally significantly less. Ideally, the volume of V2 + V3 + V4 is less than 95% of V1, and preferably, the volume of V2 + V3 + V4 is less than 90% of V1, and more preferably, the volume of V2 + V3 + V4 is less than 50% of V1, and more preferably, the volume of V2 + V3 + V4 is less than 30% of V1 the volume of V2 + V3 + V4 is less than 10% of Vi.

Figure 40 shows the fourth stage of the cycle. During the fourth stage, the crank shaft 412 is moving the piston 406 upwardly, using the connecting rod 414 which is attached to the first valve 416.

When the piston 404 starts to move upwardly (Arrow 0) from its lowest position as shown in Figure 4C, for a brief period of time, the upper entrance 452 of the U shaped passage 448 is located above the upper of the two seals 408 whilst the lower entrance 450 of the U shaped passage 448 faces into the space formed between the two seals 408 towards the outlet 446. During this brief period when the piston 406 is in this position, air located above the piston 406 is able to pass between the side of the piston 406 near the top of the piston 406 and the cylinder wail, enter the upper entrance 452 of the U shaped passage 448, pass through the U shaped passage 448, exit the lower entrance 450 of the U shaped passage 448, enter the space between the two seals 408 and then enter the outlet 446.

Subsequently, as the piston is being moved upwardly (Arrow 0) by the crank shaft 412 as shown in Figure 40, both of the entrances 450, 452 of the U shaped passage 448 of the second valve 486, remain located above both seals 408. As such, the space between the seals 408 is sealed by the side of the piston 406 and therefore the entrance to outlet 446 is sealed by the second valve 486 and as such, air is unable to pass through the outlet 446.

As the crank shaft 412 rotates to move the piston 406 upwardly inside of the cylinder 404, the crank shaft 412 causes the slide rod 438 to slide upwardly inside the slide bearing 440, moving the two valve disks 430, 432 upwardly inside of the valve chamber 418 until the two valve disks 430, 432 are in their highest position (as shown in Figure 40) with the seal 444 located remotely from lower wall of the valve chamber 418 and the upper disk 430 located against the upper wall 422 of the valve chamber 418. As the crank shaft 412 continues to rotate (Arrow M) to move the piston 406 upwardly inside of the cylinder 404, the crank shaft 412, continues to pull the slide rod 438 upwardly, the slide rod 438 pulling the valve disks 430,432 upwardly, which in turn pull the piston 406 upwardly inside of the cylinder 404 by their engagement of the upper wall 422 of the valve chamber 418. As the valve 430, 432 pulls the piston 406 upwardly, the entrance to the lower elongate tubular passage 424 is open, thus allowing air to pass between the valve chamber 418 and the compression chamber 428 of the cylinder 404 as the piston 406 moves upwardly within the cylinder 404. As such, as the piston 406 rises, air is able pass from above the piston 406 from the surrounding atmosphere, through the second upper elongate passage 436, through the valve chamber 418 and then through the lower elongate tubular passage 424 and into the compression chamber 428 of the cylinder 404. Therefore, air is able to enter the compression chamber 428 as the piston 406 moves upwardly, replenishing the air previously emitted as a pulse through the outlet 446. The air pressure inside the compression chamber 428 remains the same as that of the surrounding atmosphere as it is replenished as the piston 406 moves upwardly. This allows the compression chamber 428 to be fully replenished with air when it reaches its highest position as shown in Figure 4A.

Once the piston 406 has returned to the position shown in Figure 4A, the cycle of the piston compressor 484 is repeated as the crank shaft 412 continues to rotate (Arrow M).

Each 360 degree rotation of the crank shaft 412 results in a single cycle of the piston compressor 484. Each cycle results in a single pulse of compressed heated air entering the mixing chamber 460 of the housing 458 of the pulse spray dryer 490.

The operation of the pulse spray dryer 490 in conjunction with the piston compressor 484 will now be described.

The fluid 456 containing the solids is inserted into the tank 454 of the pulse spray dryer 490. The fluid 456 with the solids is then fed through the first pipe 462 and then through the nozzle 464 and into the mixing chamber 460 of the housing 458. The nozzle 464 atomises the fluid 456 containing the solids as it enters the mixing chamber 460. The atomised fluid 456 with the solids then mixes with the pulses of compressed heated air emitted from the second pipe 466 which are being generated by the piston compressor 484 which results in the atomised fluid 456 being vapourised.

The vapourised fluid 456 and solids enter the separation chamber 470 of the cyclonic separator 468. The vapourised fluid 456 is then separated from the solids, the solids exiting the separation chamber 470 via the third solids exit pipe 472.

The vapourised fluid 456 then passes through the fourth vapour exit pipe 474 to the vapour pump 476. As the vapourised fluid 456 passes through the fourth vapour exit pipe 474, the heat of the vapourised fluid 456 transfers to the fins 478 via the pipe 474 where it is dissipated into the surrounding environment. As such, the vapourised fluid 456 is condensed as it passes through the fourth vapour exit pipe 474 and turns back into a liquid by the time it arrives at the vapour pump 476.

The liquidised fluid 456 then passes through the fifth exit pipe 480 towards the collection tank 482 where the fluid is collected.

The operation of the piston compression pulse spray dryer will now be described in relation to desalinating a saline solution, such as sea water, where the saline solution (e.g. water with sodium chloride dissolved within it) is fed into the piston compression pulse spray dryer where the salts within the saline solution are separated from the solution. Where the saline solution is sea water, by separating the salt from the water In which it is dissolved, drinkable water can be produced.

In order to desalinate sea water, the piston compression pulse spray dryer as described above with reference to Figures 4A to 4D is used to desalinate sea water by placing sea water into the tank 454 of the pulse spray dryer 490. Ideally, the sea water has been previously filtered to remove any unwanted debris. The sea water 456 is then fed through the first pipe 462 and then through the nozzle 464 and into the mixing chamber 460 of the housing 458. The nozzle 464 atomises the sea water 456 as it enters the mixing chamber 460. The atomised sea water 456 then mixes with the pulses of compressed heated air emitted from the second pipe 466 which are being generated by the operation of the piston compressor 484 which results in the water 456 in the sea water being vapourised.

The vapourised water 456 and salt enter the separation chamber 470 of the cyclonic separator 468. The vapourised water 456 is then separated from the salt, the salt exiting the separation chamber 470 via the third solids exit pipe 472.

The vapourised water 456 then passes through the fourth vapour exit pipe 474 to the vapour pump 476. As the vapourised water passes through the fourth vapour exit pipe 474, it is condensed into liquid water.

The liquidised water 456 then passes through the fifth exit pipe 480 towards the collection tank 482 where the water is collected.

The piston compression pulse spray dryer as described above with reference to Figures 4A to 4D comprises a piston compressor 484 which uses air from the surrounding atmosphere to produce a series of pulses of compressed heated air for use in the pulse spray dryer 490. It will be appreciated that the piston compressor 484 can be utilized with (as an alternative to air) specific gases in order to produce compressed heated pulses of that specific gas. The use of specific gases, such an inert gas or a highly reactive gas, may be desirable to avoid any reaction with the fluid 456 and/or the solids contained within the fluid 456 or to specifically react with the fluid 456 and/or the solids contained within the fluid 456. The specific gas can be introduced into piston compressor 484 from a gas canister or reservoir or any such known gas storage device. Alternatively, the piston compressor 484 can be located within an environment formed from such a specific gas to ensure the piston compressor produces compressed heated pulses of such a gas.

It will also be appreciated that the piston compressor 484 can be used with any known design of pulse spray dryer 490 of a pulse combustion spray dryer. For example, the piston compressor 484 described above with reference to Figures 4A to 40 could be used with the pulse spray dryer of the pulse combustion spray drying apparatus described above with reference to Figure 2.

A second embodiment of the invention will now be described with reference to Figure 5.

Referring to Figure 5, the second embodiment of the piston compression pulse spray dryer comprises four piston compressors 484A-484D, each of which are of the same design as the single piston compressor 484 described in the first embodiment with reference to Figures 4A to 4D, and a single pulse spray dryer 490 which is the same design as the pulse spray dryer 490 described in the first embodiment with reference to Figures 4A to 4D. Each piston compressor 484A-4840 produces a series of pulses of compressed hot air, the series pulses from each of the piston compressor 484A-484D being fed into the single pulse spray dryer 490. Where the same features which are present in the first embodiment of the piston compression pulse spray dryer are present in the second embodiment, the same reference numbers have been used. As there are four piston compressors 484A-484D, the reference numbers used in relation to a particular piston compressor 484A-4840 will have a letter added, to identify which piston compressor 484A-484D it is, the first piston compressor 484A having an "A", the second piston compressor 4848 having a "B", the third piston compressor 484C having a "C", and the fourth piston compressor 484D having a "D".

Referring to Figure 5, the piston compression pulse spray dryer comprises a rotatable crank shaft 412 mounted inside of a crank housing (not shown) which is capable of rotating about an axis. Each end of the crank shaft 412 is supported by a bearing 500. Rigidly attached to one end of the crank shaft 412 is a first gear wheel 502. The first gear wheel 502 meshes with a second gear wheel 504 which is rigidly mounted on one end of a drive shaft 506. The drive shaft 506 is rotationally supported by bearings 512. A propeller 508 is mounted on the other end of the drive shaft 506. The propeller 508 is located within an air flow, such as being located on a tower to engage with a breeze or wind. The air flow through the propeller 508 causes the propellor 508 to rotate which in turn causes the first and second gears 502, 504 to rotate, which in turn causes the crank shaft 412 to rotate. The ratio of the sizes of the gears 502, 504 is chosen in order to optimise the speed of rotation of the crank shaft 412.

The crank shaft 412 comprises four offset connection sections 510. The four piston compressors 484A -484D are attached to the crank shaft 412, one piston compressor 484A4840 being connected to each of the connection sections 510. The four piston compressors 484A -484D are mounted relative to crank shaft 412 such that the axis of the crank shaft 412 extends perpendicularly to the longitudinal axes of the cylinders of the four piston compressors 484A-484D, the longitudinal axes of all of the cylinders being parallel to each other. A connecting rod 514A-514D is pivotally attached to each of the connection sections 510 of the crank shaft 412 at their upper end, the axes of pivot being parallel to but eccentrically off set from the axis of rotation of the crank shaft 412. Each of the lower ends of the connecting rods 514A-5140 is pivotally attached to a first valve formed in the top of the pistons 406A-4060 of each of the four piston compressors 484A-484D, the axes of pivot being parallel to the axis of rotation of the crank shaft 412. Rotation of the crank shaft 412 results in a linear reciprocation motion of the pistons 406A -406D inside the cylinders along the longitudinal axes of the cylinders in well know manner. Each connection section 510 is located at 90 degrees in a tangential direction around the longitudinal axis of the crank shaft 412 relative to any adjacent connection section 510 such that, when the crank shaft 412 is rotationally driven, each piston compressor 484A-484D is 90 degrees out of phase in its operating cycle in relation to the adjacent piston compressor 484A-484D.

The operation of each of single piston compressors 484A -484D is the same as that of the single piston compressor 484 in the first embodiment described above with reference to Figures 4A to 4D. All of the piston compressors 484A-4840 are connected to a single housing 458 of the single pulse spray dryer 490, each piston compressor 484A -484D being connected via a second pipe 466A -4660. Each piston compressor 484A-4840 produces a series of pulses of compressed hot air, the series of pulses from each of the piston compressors 484A-4840 being fed into the mixing chamber of the housing 458 of the single pulse spray dryer 490. As there are four piston compressors 484A-484D, each single rotation of the crank shaft 412 results in each of the piston compressors 484A-484D injecting a pulse of compressed heated air into the mixing chamber, the four pulses of compressed heated air being injected into the mixing chamber every time the crank shaft 412 makes a single rotation. As each piston compressor 484 is 90 degrees out of phase in its operating cycle in relation to its adjacent piston compressor 484A4840, the four pulses of compressed heated air enters the mixing chamber in a sequential manner at a pre-set frequency with same time period being between adjacent pulses, the time period being dependent of the rate of rotation of the crank shaft 412.

The operation of the single pulse spray dryer 490 is the same as that as the pulse spray dryer 490 in the first embodiment described in the first embodiment with reference to Figures 4A to 4D.

The advantage of the design of the piston compression pulse spray dryer in the second embodiment over that of the piston compression pulse sprayer in the first embodiment is that, every time the crank shaft 412 makes a 360 degree rotation, four pulses of compressed heated air enter the mixing chamber in the second embodiment versus a single pulse of compressed heated air entering the mixing chamber 460 in the first embodiment. This allows an increased rate of pulses of compressed heated air into the mixing chamber 460 versus the rate of rotation of the crank shaft 412.

A third embodiment of the invention will now be described with reference to Figures 6A and 68.

Referring to Figure 6A, the third embodiment of the piston compression pulse spray dryer comprises a single piston compressor 484 connected to a single pulse spray dryer (not shown) which is the same design as the pulse spray dryer described in the first embodiment with reference to Figures 4A to 4D. The piston compressor 484 produces a series of pulses of compressed hot air which are fed into the single pulse spray dryer. Where the same features which are present in the first embodiment of the piston compression pulse spray dryer are present in the third embodiment, the same reference numbers have been used.

The difference between the third embodiment of the piston compression pulse spray dryer and the first embodiment of the piston compression pulse spray dryer is the design of the piston compressor 484. In the design of the piston compressor of the first embodiment, the air flow in and out of the compression chamber 428 is controlled by two mechanical valves 416,486. In the design of the piston compressor 484 of the third embodiment, the air flow in and out of the compression chamber 428 is controlled by two electronically controlled valves 600, 602.

Referring to Figure 6A, the piston compressor 484 creates pulses of compressed heated air in a similar manner to that of the piston compressor in the first embodiment. The piston compressor 484 comprises a cylinder block 400 which is mounted below a crank shaft housing (not shown). The cylinder block 400 comprises an elongate cylinder 404 having a longitudinal axis and a uniform circular cross section, in a direction perpendicular to the axis, along the length of the cylinder 404. Slideably mounted within the cylinder 404 is a piston 406 of circular cross section of similar size to that of the cylinder 404. Mounted around the internal wall of the cylinder 404 towards the top of the cylinder 404 is a seal 604 which forms a seal between the external sidewall of the piston 406 and the side wall of the cylinder 404 and which prevents any gases from passing the seal 604. The seal 604 slides along the external sidewall of the piston 406 when the piston 406 reciprocates within the cylinder 404. The upper section of the cylinder 404 opens into a chamber 410 formed inside of the crank shaft housing. The lower section of cylinder 404 forms a compression chamber 428, the compression chamber 428 being defined by the lower internal walls of the cylinder 404 and a lower surface of the piston 406.

A rotatable crank shaft (not shown) is mounted inside of the crank housing which is capable of rotating about an axis which extends perpendicularly to the longitudinal axis of the cylinder 404. A connecting rod 414 is pivotally attached to the crank shaft at an upper end, the axis of pivot being parallel to but eccentrically off set from the axis of rotation of the crank shaft. The lower end of the connecting rod 414 is pivotally attached to the top of the piston 406, the axis of pivot being parallel to the axis of rotation of the crank shaft. Rotation of the crank shaft results in a linear reciprocation motion of the piston 406 inside the cylinder 404 along the longitudinal axis of the cylinder 404 in well know manner. A counterweight (not shown) is eccentrically mounted on the crank shaft to counteract any vibrations generated by the eccentric connection of the upper end of the connecting rod 414 as the crank shaft rotates.

The lower section of the cylinder 404 is terminated by a lower wall formed by the bottom of the cylinder block 400. A compression chamber 428 is formed inside of the lower section of the cylinder which is bounded by the lower wall of the cylinder block 400 at the bottom, by the side walls of the cylinder at the sides, and the lower surface of the piston 406 at the top.

An outlet 446 is formed through a lower section of the wall of the cylinder 404. A first pipe 608 connects between the outlet 446 and the first electronically controlled valve 602. A second pipe 466 connects between the first electronically controlled valve 602 and the pulse spray dryer 490. The pulse spray dryer 490 (not shown) is the same design as the pulse spray dryer described in the first embodiment with reference to Figures 4A to 4D.

An inlet 612 is formed through a lower section of the wall of the cylinder 404. A third pipe 614 connects between the inlet 612 and the second electronically controlled valve 600. A fourth pipe 616 connects between the second electronically controlled valve 600 and the surrounding environment.

A controller (not shown) is connected to a sensor (not shown) mounted adjacent the crank shaft. The sensor provides information to the controller as to the angular position of the crank shaft. Based on this information the controller can determine axial position of the piston 406 within the cylinder 404 and therefore the size of the compression chamber 428.

The crank shaft is rotatably driven by an external rotary force in order to reciprocatingly drive the piston 406 within the cylinder 404.

Figure 6B shows a series of graphs relating to the operation of the piston compressor 484 shown in Figure 6A. Graph 1 shows the volume Vo of the compression chamber 428 versus time t, Vo MAX indicating the maximum volume of the compression chamber 428, Vo MIN indicating the minimum volume of the compression chamber 428. Graph 2 shows the status of second electronically controlled valve 600 versus time t, OPEN indicating the second electronically controlled valve 600 is open allowing air to pass through the second electronically controlled valve 600, CLOSED indicating the second electronically controlled valve 600 is closed preventing air from passing through the second electronically controlled valve 600. Graph 3 shows the status of first electronically controlled valve 602 versus time t, OPEN indicating the first electronically controlled valve 602 is open allowing air to pass through the first electronically controlled valve 602, CLOSED indicating the first electronically controlled valve 602 is closed preventing air from passing through the first electronically controlled valve 602.

The operating cycle of the third embodiment of the piston compression pulse spray dryer will now be described.

When the piston 406 is being axially driven upwardly so that the volume of the compression chamber 428 is increasing, the second electronically controlled valve 600 is opened by the controller to allow air to pass from the surrounding environment through the fourth pipe 616, through the second electronically controlled valve 600, through the third pipe 614 and then enter the compression chamber 428 in order to replenish the air within the compression chamber 428 as it expands. As the compression chamber 428 expands, the temperature and pressure of the air within the compression chamber 428 remains the same as that of the air in the surrounding environment from which the air is being drawn. Whilst the piston 406 is being axially driven upwardly so that the volume of the compression chamber 428 is increasing, the first electronically controlled valve 602 is kept closed by the controller to prevent air from passing through it.

When the piston 406 is at its highest position so that the volume of the compression chamber 428 is at its maximum Vo MAX, the second electronically controlled valve 600 is closed by the controller to prevent air from passing through it. The first electronically controlled valve 602 is maintained closed by the controller to prevent air from passing through it whilst the piston 406 is in its highest position.

When the piston 406 is being axially driven downwardly so that the volume of the compression chamber 428 is decreasing, the second electronically controlled valve 600 is kept closed by the controller to prevent air from passing through it. Whilst the piston 406 is being axially driven downwardly so that the volume of the compression chamber 428 is decreasing, the first electronically controlled valve 602 is still kept closed by the controller to also prevent air form passing through it. As such, the air in the compression chamber 428 is compressed increasing both its pressure and temperature as it is compressed.

When the piston 406 is at its lowest position so that the volume of the compression chamber 428 is at its minimum Vo MIN and the pressure and temperature of the air inside of the compression chamber 428 are at their maximum, the first electronically controlled valve 602 is opened the controller to allow a compressed heated pulse of air to pass through the first pipe 608, through the first electronically controlled valve 602, through the second pipe 466 and then enter the pulse spray dryer 490 so that the pulse spray dryer 490 can operate in the same manner as described above in the first embodiment with reference to Figures 4A to 40. The second electronically controlled valve 600 is maintained closed by the controller whilst the first electronically controlled valve 602 is open.

The first electronically controlled valved is then closed and the cycle is then repeated.

A fourth embodiment of the invention will now be described with reference to Figures 7A and 7B.

Referring to Figure 7A, the third embodiment of the piston compression pulse spray dryer comprises a single piston compressor 484 connected to a single pulse spray dryer 490 (not shown) which is the same design as the pulse spray dryer described in the first embodiment with reference to Figures 4A to 40. The piston compressor 484 produces a series of pulses of compressed hot air which are fed into the single pulse spray dryer 490. Where the same features which are present in the first embodiment of the piston compression pulse spray dryer are present in the third embodiment, the same reference numbers have been used.

The difference between the fourth embodiment of the piston compression pulse spray dryer and the first embodiment of the piston corn pression pulse spray dryer is the design of the piston compressor 484. In the design of the piston compressor of the first embodiment, the air flow in and out of the compression chamber 428 is controlled by two mechanical valves 416, 486. In the design of the piston compressor 484 of the third embodiment, the air flow in and out of the compression chamber 428 is controlled by a three way electronically controlled valve 700.

Referring to Figure 7A, the piston compressor 484 creates pulses of compressed heated air in a similar manner to that of the piston compressor in the first embodiment. The piston compressor 484 comprises a cylinder block 400 which is mounted below a crank shaft housing (not shown). The cylinder block 400 comprises an elongate cylinder 404 having a longitudinal axis and a uniform circular cross section, in a direction perpendicular to the axis, along the length of the cylinder 404. Slideably mounted within the cylinder 404 is a piston 406 of circular cross section of similar size to that of the cylinder 404. Mounted around the internal wall of the cylinder 404 towards the top of the cylinder 404 is a seal 704 which forms a seal between the external sidewall of the piston 406 and the side wall of the cylinder 404 and which prevents any gases from passing the seal 604. The seal 704 slides along the external sidewall of the piston 406 when the piston 406 reciprocates within the cylinder 404. The upper section of the cylinder 404 opens into a chamber 410 formed inside of the crank shaft housing. The lower section of cylinder 404 forms a compression chamber 428, the compression chamber 428 being defined by the lower internal walls of the cylinder 404 and a lower surface of the piston 406.

An outlet 446 is formed through a lower section of the wall of the cylinder 404. A first pipe 708 connects between the outlet 446 and the three way electronically controlled valve 700. A second pipe 466 connects between the three way electronically controlled valve 700 and the pulse spray dryer 490. The pulse spray dryer 490 (not shown) is the same design as the pulse spray dryer described in the first embodiment with reference to Figures 4A to 4D. A third pipe 710 connects between the three way electronically controlled valve 700 and the surrounding environment.

Figure 78 shows a series of graphs relating to the operation of the piston compressor 484 shown in Figure 7A. Graph 1 shows the volume Vo of the compression chamber 428 versus time t, Vo MAX indicating the maximum volume of the compression chamber 428, Vo MIN indicating the minimum volume of the compression chamber 428. Graph 2 shows the status of the three way electronically controlled valve 700 versus time t in relation to the connectivity of the first pipe 708 and the third pipe 710, OPEN indicating the connection of the three way electronically controlled valve 700 between the first pipe 708 and the third pipe 710 is open allowing air to pass through the three way electronically controlled valve 700 between these two pipes, CLOSED indicating the connection of the three way electronically controlled valve 700 between the first pie 708 and the third pipe 710 is closed preventing air from passing through the three way electronically controlled valve 700 between these two pipes. Graph 3 shows the status of the three way electronically controlled valve 700 versus time t in relation to the connectivity of the first pipe 708 and the second pipe 466, OPEN indicating the connection of the three way electronically controlled valve 700 between the first pipe 708 and the second pipe 466 is open allowing air to pass through the three way electronically controlled valve 700 between these two pipes, CLOSED indicating the connection of the three way electronically controlled valve 700 between the first pipe 708 and the second pipe 466 is closed preventing air from passing through the three way electronically controlled valve 700 between these two pipes.

The operating cycle of the fourth embodiment of the piston compression pulse spray dryer will now be described.

When the piston 406 is being axially driven upwardly so that the volume of the compression chamber 428 is increasing, the three way electronically controlled valve 700 is opened by the controller to allow air to pass from the surrounding environment through the third pipe 710, through the three way electronically controlled valve 700, through the first pipe 708 and then enter the compression chamber 428 in order to replenish the air within the compression chamber 428 as it expands. As the compression chamber expands, the temperature and pressure of the air within the compression chamber 428 remains the same as that of the air in the surrounding environment from which the air is being drawn. Whilst the piston 406 is being axially driven upwardly so that the volume of the compression chamber 428 is increasing, the three way electronically controlled valve 700 prevents air from passing through the second pipe 466.

When the piston 406 is at its highest position so that the volume of the compression chamber 428 is at its maximum Vo MAX, the three way electronically controlled valve 700 is closed by the controller to prevent air from passing through it via any of the pipes 708, 466, 710.

When the piston 406 is being axially driven downwardly so that the volume of the compression chamber 428 is decreasing, the three way electronically controlled valve 700 is kept closed by the controller to prevent air from passing through any of the pipes 708, 466, 710. As such, the air in the compression chamber 428 is compressed increasing both its pressure and temperature as it is compressed.

When the piston 406 is at its lowest position so that the volume of the compression chamber 428 is at its minimum Vo MIN and the pressure and temperature of the air inside of the compression chamber 428 are at their maximum, the three way electronically controlled valve 700 is opened by the controller to allow a compressed heated pulse of air to pass through the first pipe 708, through the three way electronically controlled valve 700, through the second pipe 466 and then enter the pulse spray dryer 490 so that the pulse spray dryer 490 can operate in the same manner as described above in the first embodiment with reference to Figures 4A to 40. Whilst the pulse of heated compressed air passes into the pulse spray dryer 490, the three way electronically controlled valve 700 maintains the second pipe 710 closed.

The cycle is then repeated.

Claims

Clatins 1 A piston compressor for a pulse spray dryer comprising: a cylinder block (400); a cylinder(404) formed in the cylinder block (400); at least one piston (406) slideably mounted within the cylinder (404); wherein a compression chamber (428) is formed between the internal walls of the cylinder (404) and at least one surface of the at least one piston (406), the volume of the compression chamber (428) being dependent on the position of the at least one piston (406) within the cylinder (404); a reciprocating drive mechanism (412) which reciprocatingly drives the at least one piston (406) within the cylinder (404) to change the volume the of the compression chamber (428); at least one valve (416; 486; 600; 602; 700) which is capable of allowing a gas to enter and/or exit the compression chamber (428); at least one timing device (416; 486) to operate the at least one valve (416; 486; 600; 602; 700); characterised in that when the reciprocating drive mechanism (412) is reciprocatingly driving the at least one piston (406) within the cylinder (404) to change the volume the of the compression chamber (428), the least one timing device (416; 486) operates the at least one valve (416; 486; 600; 602; 700), at predetermined time periods, to enable the at least one valve (416; 486; 600; 602; 700) to: 1) allow the gas to enter the compression chamber (428) in order for it to be compressed by the reciprocating movement of the at least one piston (406); and 2) allow the gas to exit the compression chamber (428) when the gas has been compressed and the pressure and temperature of the gas has been increased.
2 A piston compressor as claimed in claim 1 wherein the at least one valve (416; 486; 600; 602; 700) allows the gas to exit the compression chamber (428) when the gas has been compressed and the pressure and temperature of the gas has been increased in the form of a pulse.
3 A piston compressor as claimed in any of the previous claims wherein there is at least one outlet (446) through which gas can exit the compression chamber (428); wherein, preferably, the at least one valve (486; 602; 700) is connected to the at least one outlet (446), and/or; wherein preferably the outlet (446) is a passageway formed through the cylinder block (400) which is capable of connecting to the compression chamber (428).
4 A piston compressor as claimed in any of the previous claims wherein there is at least one inlet (436, 418, 424; 612) through which gas can enter the compression chamber (428); wherein, preferably, the at least one valve (416; 600; 700) is connected the at least one inlet (436, 418, 424; 612); and/or; wherein, preferably, the inlet (436, 418, 424; 612) is a passageway formed through the cylinder block (400) which is capable of connecting to the compression chamber (428).
A piston compressor as claimed in any of the previous claims wherein, when the reciprocating drive mechanism (412) is reciprocatingly driving the at least one piston (406) within the cylinder (404) to change the volume the of the compression chamber (428), the least one timing device (416; 486) operates the at least one valve (416; 486; 600; 602; 700) to enable the at least one valve (416; 486; 600; 602; 700) to allow the gas to: 1) enter the compression chamber (428) when the volume of the compression chamber (428) is increasing or when the volume of the compression chamber (428) is at its maximum; and/or 2) exit the compression chamber (428) when the pressure and temperature of the gas has been increased; and/or 3) exit the compression chamber (428) when the volume of the compression chamber (428) is decreasing or when the volume of the compression chamber is at its minimum (428) and the pressure and temperature of the gas has been increased.
6) A piston compressor as claimed in any of the previous claims wherein the pressure of the gas when it enters the compression chamber (428) is substantially less than when it exits the compression chamber (428) and the temperature of the gas when it enters the compression chamber (428) is substantially less than when it exits the compression chamber (428).
7) A piston compressor as claimed in any of the previous claims wherein the at least one valve (416;486; 600; 602; 700) is capable of connecting to a pulse spray dryer (490) so that, when the gas exits the compression chamber (428), it enters the pulse spray dryer (490).
8) A piston compressor as claimed in any one of the previous claims wherein the at least one timing device (416; 486; 404; 406) comprises the at least one valve (416; 486)- 9) A piston compressor as claimed in any one of the previous claims wherein the at least one timing device (416; 486; 404; 406) opens and closes the at least one valve (416; 486, 600; 602; 700) dependent on the direction of movement of the at least one piston (406) within the cylinder (404); and preferably the at least one timing device (416; 486; 404; 406) opens the at least one valve (416; 486; 600; 602; 700) when the at least one piston (406) is sliding within the cylinder (404) to increase the volume of the compression chamber (428) and the at least one timing device closes the at least one valve when the at least one piston (406) is sliding within the cylinder (404) to decrease the volume of the compression chamber (428).10)A piston compressor as claimed in any one the previous claims wherein the at least one timing device opens and closes the at least one valve dependent on the position of the piston within the cylinder, and preferably the at least one timing device opens the at least one valve at least when the at least one piston is located within the cylinder when the volume of the compression chamber is at its minimum.11)A piston compressor as claimed in any one of the previous claims wherein the at least one valve is either a purely a mechanical valve or an electronically controlled valve (600, 602, 700) and preferably a three way electronically controlled valve.12)A piston compressor as claimed in any one of the previous claims wherein there are two valves, a first valve which enables gas to enter the compression chamber and a second valve which enables the gas to exit the compression chamber.13)A piston compressor as claimed in claim 12 wherein the first valve enables the gas to enter the compression chamber when the movement of the at least one piston in the cylinder results in an increase the volume of the compression chamber and the second valve enables the gas to exit the compression chamber when the position of the at least one piston in the cylinder is such that the volume of the compression chamber is at its minimum.14)A piston compressor as claimed in any one of the previous claims wherein the reciprocating drive mechanism connects to the at least piston via the at least one valve.15)A piston compressor as claimed in any one of the previous claims wherein the at least one valve is a mechanical valve mounted within the at least one piston and comprises: a valve chamber (418) formed in the at least one piston (406); a tubular passage (424) which extends from the valve chamber (418) through the at least one piston (406) to the compression chamber (428); a second upper elongate tubular passage (436) which extends from the valve chamber (418) through the at least one piston (406) to the upper surface of the at least one piston (406) and which is capable of allowing gas to freely pass between the valve chamber (418) and a space above the piston (406); at least one valve disk (430, 432) moveably mounted within the valve chamber (418) and moveable between a first position and a second position, wherein when the at least one valve disk is in its first position, it seals the tubular passage (424) to prevent gas from passing through it and when the at least one valve disk is in its second position, it opens the tubular passage (424) to allow gas to pass through it; a slide rod 438 connected to the at least one valve disk, movement of the slide rod moving the at least one valve disk between its two positions.16)A piston compressor as claimed in claim 15 wherein there is further provided another first upper tubular passage (434) which extends from the valve chamber (418) through the at least one piston (406) to the upper surface of the at least one piston (406), wherein the first upper elongate passage (434) extends parallel to and is co-axial with the longitudinal axis of the cylinder (404); wherein the second upper elongate passage (436) extends parallel to but is offset from the longitudinal axis of the cylinder (404); wherein the slide rod (438) is slidably mounted inside of a side bearing (440) mounted within the first upper tubular passage (434); wherein the slide rod (438) extends parallel to and is co-axial with the longitudinal axis of the cylinder (404) and is capable of sliding axially along its longitudinal axis within the slide bearing (440).17)A piston compressor as claimed in any of claims 15 or 16 wherein the upper end of the slide rod (438) is pivotally attached to the lower end of a connecting rod (414) of the reciprocating drive mechanism.18)A piston compressor as claimed in any one claims 15 to 17 wherein there is a seal (444) is mounted on the at least one valve disk (430, 432) wherein when the at least one valve disk (430, 432) is in its first position, the seal (444) is sandwiched between the at least one valve disk (439, 432) and a side wall (420) of the valve chamber (418) to seal the entrance to the lower elongate tubular passage (424).19)A piston compressor as claimed in any of the previous claims wherein the reciprocating drive mechanism comprises a crank shaft (412) connected to the slide rod; wherein, when the crank shaft (412) rotates to slide the at least one piston (406) inside of the cylinder (404), the crank shaft (412) first causes the slide rod (438) to slide inside the slide bearing (440) to move the at least one valve disk (430, 432) inside of the valve chamber 418 between its two positions, before it causes the at least one piston to slide within the cylinder.20)A piston compressor as claimed in any one of the previous claims wherein the at least one valve is a mechanical valve which comprises: an outlet (446) formed through the wall of the cylinder (404) which faces towards the side of the at least one piston; at least one seal (408) sandwiched between the side of the at one piston and the wall of the cylinder and which prevents gas from passing to or from, above or below, the at least one piston, between the side of the at least one piston and the wall of the cylinder and enter or exit the outlet; a U-shaped passage (448) formed through the at least one piston having a lower entrance (450) at one end of the U shaped passage (448) formed in the side wall of the at least one piston (406) and an upper entrance (452) at the other end of the U shaped passage formed in the side wall of the at least one piston (406) and which is located axially above the lower entrance (450); wherein, when the at least one piston (406) reciprocatingly slides up and down within the cylinder, the U-shaped passage is capable of enabling gas to pass around the at least one seal and allow gas to pass to or from, above or below, the at least one piston, and enter or exit the outlet; wherein, during certain parts of the operating cycle, gas is able to exit the compression chamber, pass between the side of the piston (406), pass around the at least one seal 408 by entering one of entrances (450, 452) of the U shaped passage (448), pass through the U shaped passage (448) and exit the other entrance (450, 452) of the U shaped passage (448), and then enter the outlet (446).21) A piston compression pulse spray dryer comprising: at least one piston compressor as claimed in any of claims 1 to 20 and at least one pulse spray dryer; wherein the at least one piston compressor provides a series of pulses of compressed heated gas to the at least one pulse spray dryer.22)A piston compression pulse spray dryer as claimed in claim 21 wherein the at least one pulse spray dryer (490) comprises: a tank (454) for a fluid (456) containing the solids; a housing (458) which forms a mixing chamber (460); a supply passage (462) which connects the tank (454) to the mixing chamber (460); a separator 468 which forms a separation chamber 470 which comprises a first exit 472 and a second exit (474); a separator passage which connects the mixing chamber to the separation chamber; wherein the at least one piston compressor is connected to the mixing chamber and is capable of providing a series of pulses of compressed heated gas to the mixing chamber; wherein the tank is capable of providing the fluid with solids to the mixing chamber via the supply passage (462); wherein, when the at least one piston compressor provides a series of pulses of compressed heated gas to the mixing chamber and the tank provides fluid with solids to the mixing chamber, the pulses of compressed heated gas mix with the fluid with solids in the mixing chamber to form a mixture of vapourised fluid and solids; wherein the mixture of vapourised fluid and solids exits the mixing chamber and enters the separator via the separator passage where the vapourised fluid is separated from the solids; wherein the solids exit the first exit and the vapourised fluid exits the second exit.23)A piston compression pulse spray dryer as claimed in either of claims 21 or 22 wherein the combined volumes of the compression chamber at its smallest volume V2 and the volume V3 of the interconnection passageway between the compression chamber 428 and the mixing chamber 460 is less than the volume of the compression chamber 428 at its maximum volume V1, and ideally significantly less, and preferably, the volume of V2 + V3 is less than 95% of V1, and preferably, the volume of V2 + V3 is less than 90% of V1, and more preferably, the volume of V2 + V3 is less than 50% of V1, and more preferably, the volume of V2 + V3 is less than 30% of V1 the volume of V2 + V3 is less than 10% of V1.24)A piston compression pulse spray dryer as claimed in any one of claims 21 to 23 wherein the combined volumes of the compression chamber 428 at its smallest volume V2, the volume V3 of the interconnection passageway between the compression chamber 428 and the mixing chamber 460 and the volume V4 of the mixing chamber 460 needs to be less than the volume of the compression chamber 428 at its maximum volume V1, and ideally significantly less, and preferably the volume of V2 + V3 + V4 is less than 95% of V1, and preferably, the volume of V2 + V3 + V4 is less than 90% of V1, and more preferably, the volume of V2 + V3 + V4 is less than 50% of V1, and more preferably, the volume of V2 + V3 + V4 is less than 30% of V1 the volume of V2 + V3 + V4 is less than 10% of Vi.25) A method of desalinating a salt solution using a piston compression pulse spray dryer according to any one of claims 21 to 24 wherein the method comprises the steps of: placing water with a salt dissolved within it, preferably sea water, as the fluid with the solids in the tank, operating the piston compression pulse spray dryer so that the salt exits the first exit and water exits the second exit.