AU2009200546A1 - Heat Exchanger - Google Patents

Description

AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION Standard Patent Applicant(s): AgResearch Limited Invention Title: Heat Exchanger The following statement is a full description of this invention, including the best method for performing it known to me/us: P80210 AU PatSetFling Application 2009-2-9.doc (M) -2 HEAT EXCHANGER TECHNICAL FIELD The invention relates to a heat exchanger. More specifically, the invention relates to a 5 gas to gas shell and tube heat exchanger. BACKGROUND ART Heat exchangers, of which there are many types are employed to heat or cool fluids including liquids and gases. Typically, hot fluid passes through one side of the 10 exchanger whilst a cooler second fluid passes through a separate side of the exchanger and heat is transferred from one fluid to the other. Heat exchangers are used in many processing applications such as in food processing, textile processing, petrochemical processing and wood pulp processing. 15 One well-known type of heat exchanger is a shell and tube heat exchanger. These consist of one or more heat exchanger elements which are interconnected to form a flow system. The heat exchanger elements include one or more heat transfer tubes surrounded by an outer shell or jacket tube or casing. The heat transfer tubes are interconnected with one another to form product flow inserts which are in turn 20 connected by means of product pipe bends in order to circulate the product which is to be heated or cooled, depending on the process for which the heat exchanger is to be used. The heat exchanger tubes are enclosed in a shell, jacket tube or casing which also encloses the heat transfer medium which may consist of gases such as air or steam or liquids such as water. 25 As may be appreciated by those skilled in the art, despite being well known and used, shell and tube heat exchangers have many drawbacks. Examples of problems in the art include: 3 0 * Maximising heat transfer efficiency whilst also maximizing fluid flow and avoiding fouling; N.\Melbourne\Caaes\Patent\8Ooo-ao999\peO210.AU\Specis\Amended Specification.doc 11/02/09 - 3 * Loss of heat transfer efficiency due to not using true counter-current flows (existing exchangers use co-current, cross-current or partial counter-current operation. * High manufacturing costs through needing rolled tubes, large amounts of 5 materials and labour requirements for example to weld the various joints. " Low commercial need to retrofit existing processing plants with new heat exchangers owing to low rates of internal rate of return and high cost of manufacture and installation. 10 Finally, shell and tube heat exchangers typically require use of supports inside the shell to hold the tubes in place. During processing, the supports effectively act as baffles to flow of the fluid through the shell side of the heat exchanger. Whilst baffling may assist in creating a more turbulent flow through the shell side, the pressure 15 required to force the fluid through the shell can be significant and therefore requires larger pumping equipment (and subsequent higher capital and running costs). By way of example, US 5,203,405 teaches of a shell and tube heat exchanger design that recognises the problem of requiring a tube support at the U-bend and the 20 difficulties that can cause in terms of pressure drop and flow of fluid on the shell side. The solution proposed in the '405 patent is the use of an annular distributor band through which shell side fluid can pass therefore in part by-passing the U-bend. This solution does require additional cost and still does not eliminate the need for a U-bend in the tubes. In addition the flow patterns described are largely co-current therefore not 25 maximising the heat transfer efficiency. It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice. 30 All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art 35 publications are referred to herein, this reference does not constitute an admission that N:\Melbourne\Cases\Patent\80000-80999\P8021o.AU\Speci\Amended Specification.doc 11/02/09 any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country. It is acknowledged that the term 'comprise' may, under varying jurisdictions, be 5 attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, the term 'comprise' shall have an inclusive meaning - i.e. that it will be taken to mean an inclusion of not only the listed components it directly references, but also other non-specified components or elements. This rationale will also be used when the term 'comprised' or 'comprising' is 10 used in relation to one or more steps in a method or process. Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only. 15 DISCLOSURE OF INVENTION According to one aspect of the present invention there is provided a shell and tube heat exchanger to exchange heat energy between two fluids including: a shell having a first and second distal end and a first and second shell 20 chamber partitioned using a longitudinal baffle sealing from the first distal end to prior to the second distal end; at least one opening between the first and second chamber located prior to the second distal end; 25 a first and second bank of tubes located within the first and second chambers; tube header plates disposed transversely to the shell at either distal end of the shell used to retain the tube banks and divided into two halves by the longitudinal baffle with each half corresponding to each chamber in the shell; 30 a chamber linking the first bank of tubes in the first chamber with the second bank of tubes in the second chamber; N:\Melbourne\Cases\Patent\80000-90999\P8021O.AU\Specis\Amended Specification.doc 11/02/09 -5 at least one first shell opening located adjacent the first distal end of the shell and located such that shell side fluid enters or exits the first opening in a transverse direction to the tube bank in the first chamber; 5 at least one second shell opening located adjacent the first distal end of the shell and opposing the first shell opening located such that shell side fluid enters or exits the at least one second opening in a transverse direction to the tube bank in the second chamber. 10 Preferably, the chamber linking the first bank of tubes in the first chamber with the second bank of tubes in the second chamber has a U-shaped cross section. It should be appreciated from the above description that the inventors have developed an alternative configuration of heat exchanger. In particular, the chamber used to transfer tube side fluid between tube banks in each shell chamber has several 15 advantages over the art. For example, U-bends in the tubes are not required removing significant capital and manufacturing costs. A further advantage of having the chamber is that unlike U-bend tube configurations, there is no requirement for tube supports therefore also reducing manufacturing costs. As noted in the prior art, tube supports can act as baffles and increase pressure drop therefore, the avoidance of 20 supports also has the added benefit of reducing flow constraints. Preferably, the two fluids are predominantly gas streams including: air, steam, and combinations thereof. It should be appreciated though that other gases may be used without departing from the scope of the invention. 25 Preferably, the shell is shaped as a cylinder, tube, or may be a cuboid or rectangular box shape. Preferably, the first shell opening is a single opening along the width of the first tube 30 bank in the first chamber. Preferably, the second shell opening is a single opening along the width of the second tube bank in the second chamber. N:\Melbourne\Casea\Patent\80000-80999\P80210.AU\Specie\Amended Specification.doc 11/02/09 - 6 Preferably, the first and second tube banks have an equivalent heat transfer area. More preferably, the width, depth and height the first and second tube banks and shell chambers enclosing the tube banks are approximately symmetrical. 5 Preferably, the opening between the first and second chamber is a single opening along the width of both the first and second tube banks. It should be appreciated that by using wide openings, smooth flow of fluid is encouraged in order to minimise pressure drop through the exchanger. Since the 10 amount of pressure drop influences the size of fan or fans required (and hence capital and running costs), the lower the pressure difference the lower the capital and running costs of the unit. Note that reference has been made to fans given that in preferred embodiments, the fluids are predominantly gases. It should be appreciated that where liquids are used, pumps may be used instead of fans and that similar issues 15 surrounding cost described above applies to pumps as well. Preferably the tube header sheet seals the shell side from the tube side preventing mixing of shell side fluid with tube side fluid and vice versa. In one embodiment, sealing is achieved by welding the tubes to the tube header sheets. In a preferred 20 embodiment, sealing is achieved using a sealant. Most preferably, sealant is applied on both the exterior surface and interior surface of the tube header sheet. For the purposes of this specification, the term 'sealant' refers to viscous materials that change state to become solid, once applied, and prevent the penetration of fluids such 25 as water or air from one location through a barrier into another. In one particular embodiment, the tubes endings on the exterior of the tube header plate sit proud of the plate and sufficient sealant is added in the recessed area around the tubes such that the level of sealant is flush with the tube endings. In the same 3 0 embodiment, sufficient sealant is added to the interior of the tubes to form a layer of sealant between the interior of the plate and around the tubes. Preferably, the sealant is an acryl sealant, silicone sealant, polysulfide sealant, polyurethane sealant and the like. As may be appreciated, the choice of sealant 35 depends on the process parameters and fluids used. In embodiments where air is the N:\Mebourne\Caoee\Patent\80000-80999\PO0210.AU\Spec is \Amended Specification.doc 11/02/09 - 7 fluid and the processing temperatures vary from -50*C to 250*C, preferred sealants include flowable silicon sealants. It should be appreciated from the above description that the inventors have surprisingly 5 found that it is possible to use sealant instead of prior art techniques such as welding to effectively seal the tube side fluid from the shell side fluid. Sealants used have been found to have sufficient strength, flexibility, and durability to withstand use in the heat exchanger of the present invention. 10 In preferred embodiments, the tubes used in the present invention are a thin gauge material. In traditional heat exchanger designs, the material used is a thicker gauge to allow for welding and/or extrusion. In the present invention, the tubes are able to be a thin gauge such that they can be roll-formed rather than extruded. The tubes once rolled are held together preferably using a weld along the tube seam. Alternatively a 15 lap joint could be formed along the tube seam in which case the lap joint may be further sealed by application of sealant along the seam of the joint. The sealant may be applied to both the exterior and interior surfaces of the tube seam. The sealant used may be the same as that used to seal the tube header sheets. 20 It should be appreciated that the tubes of the present invention as described above are of benefit as they are simpler and cheaper to manufacture, are less expensive due to thinner gauge material used and also have a lower mass. Preferably, the chamber for transfer of tube side fluid is hollow and can be fitted and 25 removed easily to assist with cleaning and servicing of the interior of the tubes. Easy removal and re-fitting makes this chamber extremely useful in cleaning operations. By removing the chamber, the tubes can be physically cleaned and visually inspected quickly and easily. By contrast many existing heat exchangers can only be cleaned chemically as it is difficult to clean around U-bends using a brush or similar device and 3 0 the U-bend also makes it difficult to check the tubes visually for obstructions, scaling and the like. In one embodiment, a tube restraint mechanism is used to laterally restrain the tubes. Preferably, the tube restraint mechanism is a suitably shaped flat bar which is inserted 35 approximately mid-height between the tubes and rotated sufficiently to locate and N:\Melbourne\Cases\Patent\80000-80999\P0210.AU\Specis\Amended Specification.doc 11/02/09 - 8 laterally restrain the tubes. The aim of the tube restraint is to maintain tube-to-tube clearances and locate the tube bank centrally in the shell. It should be appreciated that a tube restraint may not be required in smaller configurations or alternatively, multiple tube restraints may be required in larger configurations. 5 In a further embodiment, the exchanger includes a mechanism to allow for a differential in thermal expansion between the tube bank and the shell. In one preferred embodiment the mechanism may be a pneumatically activated bellows working in conjunction with a guide pin. The bellows adjust for the longitudinal expansion of the 10 tubes against the shell while the guide pin maintains the tube bank centrally in the shell chamber. In preferred embodiments, the flow of fluid through the heat exchanger is true counter current wherein the shell side fluid enters the shell opening on the side opposing the 15 tube bank into which the tube side fluid enters. As should be appreciated, true counter current flow is preferable due to the heat transfer gains demonstrated by this flow. Preferably, the shell exterior may be insulated to minimise heat loss. 2 0 In a preferred embodiment, the heat exchanger of the present invention is positioned such that the first distal end of the exchanger is at the top and the second distal end of the shell and U-shaped cross section chamber is at the bottom of the exchanger. In preferred embodiments the exchanger shell is cuboid and the height of the shell and tube length is approximately 6-8 times longer than the depth of the exchanger and the 25 width is approximately 2-3 times the depth of the exchanger. It should be appreciated from the above description that there is described an improved shell and tube heat exchanger design including modified tube design, lower mass, modified methods to assemble the exchanger using sealant rather than welding 30 and true counter-current flow arrangement. The advantages which should be apparent to those skilled in the art include an increased heat transfer efficiency, lower manufacturing costs through increased manufacturing speeds, simplified installation and the ability to cost effectively retrofit the exchanger into existing plants as well as use in new plants. 35 N:\Melbourne\Casea\Patent\80000-80999\P0210.AU\Speci \Amended Specification.doc 11/02/09 - 9 BRIEF DESCRIPTION OF DRAWINGS Further aspects of the present invention will become apparent from the ensuing description which is given by way of example only and with reference to the accompanying drawings in which: 5 Figure 1 shows an overall perspective view of the heat exchanger in one embodiment of the present invention; Figure 2 shows a cross sectional elevation view of the heat exchanger; 10 Figure 3 shows a perspective view of the top section of the heat exchanger; Figure 4 shows a plan view of the top section of the heat exchanger; 15 Figure 5 shows a perspective partial cross sectional view of a tube/tube plate assembly used in the heat exchanger; Figure 6 shows a detailed cross sectional view of a tube/tube plate assembly used in the heat exchanger; 20 Figure 7 7a shows a detail plan view of one tube used in the heat exchanger, 7b shows close up view of lap joint; Figure 8 shows a horizontal cross sectional view through the tube bank and 25 associated shell chamber showing a tube restraint mechanism used in the heat exchanger; Figure 9 shows a vertical cross section of a tube restraint mechanism used in the heat exchanger; 30 Figure 10 shows cross-sectional view of a pneumatic bellows and one of its associated guide pins as used in the heat exchanger; Figure 11 shows a perspective view of the guide pin as used in the heat 35 exchanger; N:\Melbourne\Caoes\Patent\80000-80999\P8021O.AU\Specis\Amended Specification.doc 11/02/09 - 10 Figure 12 shows a process flow diagram of the heat exchanger retrofitted into an existing spray dryer assembly used in dairy processing; Figure 13 shows a graph of the modelled effect of energy cost on IRR at inlet 5 conditions of 30*C and 30% RH; Figure 14 shows a graph of the modelled effect of inlet air temperature conditions on IRR at an energy cost of $8.00/GJ; 10 Figure 15 shows a graph of the modelled effect of inlet air temperature conditions on percentage of dryer heat recovered; Figure 16 shows a graph of a typical temperature log covering 10 days during a trial time period, showing the intermittent nature of the dryer operation; 15 and, Figure 17 shows a graph illustrating the effect of shell-side flow rate on overall heat transfer coefficient. 20 BEST MODES FOR CARRYING OUT THE INVENTION The invention is now described with reference to two examples. In the first example a general description of the heat exchanger is described including details on calculated efficiencies. The second example describes a pilot trial using the heat exchanger of the present invention. 25 EXAMPLE 1 The inventors have designed a modified shell and tube heat exchanger (indicated generally by arrow 1) using light gauge tubing 19 in a light-weight, largely bonded (as opposed to welded) assembly. The flow paths of the fluids used in the exchanger are 3 0 also modified to existing shell and tube heat exchanger designs. More specifically, Figure 1 shows perspective view and Figure 2 shows a front elevation cross section view of a typical installation layout of a preferred embodiment of the heat exchanger 1. N:\Melbourne\Caoes\Patent\80000-80999\P8021.AU\Specis\Amended Specitication.doc 11/02/09 - 11 The heat exchanger includes a shell 2 with a first distal end 3 and a second distal end 4. The shell 2 includes a first chamber 5 and a second chamber 6. The two chambers 5, 6 are partitioned via a longitudinal baffle 7. There is an opening 8 in the baffle 7 5 between the first 5 and second chambers 6 located at the second distal end 4 of the exchanger 1. A first 9 and second 10 bank of tubes is located between the first and second chamber 5, 6. Tube header plates 11 are located at the first and second distal ends 3, 4 of the heat exchanger 1. These header plates 11 fix the tube banks 9, 10 in place and are divided into two halves by the longitudinal baffle 7 with each half 10 corresponding to the shell chambers 5, 6. A U-shaped cross section chamber 12 links the tube bank 9 in the first chamber 5 to the second tube bank 10 in the second chamber 6. The shell 2 has a first opening 13 located at the first distal end 3 of the shell 2 opening into the first chamber 5 and a second opening 14 located at the first distal end 3 and opposing the first opening 13 of the shell 2 opening into the second 15 chamber. The shell may include bracing 21 around the mid-section of the shell 2 to aid in structural stability. This bracing may also support a tube restraint mechanism (not shown). The shell 2 may also be covered in insulating material 22 to help reduce heat 20 loss. Referring to Figures 3 to 6, the tube header 11 includes banks of tubes 9, 10 located within the shell chambers 5, 6 located within the shell 2. Individual tubes 19 and the header plate 11 are sealed together using a sealant 17, 18 as shown in Figures 5 and 25 6. The tubes 19 pass through the header plate 11 and then a sealant 17, 18 is inserted around the tube 19 and header plate exterior 15 and interior 16. Optionally, only one side 15, 16 may be sealed but for greater sealing action, both sides 15, 16 may be sealed. 30 Referring to Figures 7A and 7B, the tubes 19 are manufactured using a thin gauge material such as stainless steel in dairy or food processing applications. The material is rolled into a tube shape 19 and a seam weld (not shown) or a lap joint 20 is used to fasten the tube together as shown in Figures 7A and 7B. The lap joint 20 is sealed using a bonding sealant (not shown) along the inside, outside or both of the joint 20. 35 N:\Melbourne\Cases\Patent\60000-80999\P60210.AU\Specie\Amended Specification.doc 11/02/09 - 12 Referring to Figures 8 and 9, a tube restraint mechanism shown generally by arrow 60 is shown. Figure 8 shows a horizontal cross section plan view of the restraint 60 and Figure 9 shows a corresponding front elevation view of the restraint 60. In this example, the restraint 60 is formed by multiple bars 61, 62 running between the tubes 5 63. The bars 61,62 have concave shaped sections 64 to accept the tubes 63 as shown in Figure 8. The bars 61,62 also include apertures 65 to reduce the flow resistance on the shell side by fluids (not shown) passing the bars 61,62. In this example, the bars 61,62 are positioned approximately mid-way along the length of the tubes 63. The aim of the restraint mechanism 60 is to fix the tubes 63 in place. The 10 restraint 60 may also be used to stiffen the tube 63 assembly. Referring to Figures 10 and 11, a mechanism 70 is shown to address any differential in thermal expansion between the shell 71 and the tubes 72. In this example, the mechanism is a bellows unit 73 working in conjunction with guide pins 74 to allow for 15 the differential expansion between the tube bank 72 and shell chamber 71. A computer model was produced of the heat exchanger of the present invention used in a dairy operation where heat from air leaving a spray dryer was exchanged with incoming air into the spray dryer (process flow diagram as shown in Figure 12). 20 As shown in Figure 12, the spray dryer operation included the heat exchanger of the present invention 1, a spray dryer 50, a fluid bed dryer 51, a baghouse 52, and a heater 53. Exhaust air 54 from the spray dryer 50 was passed through the heat exchanger 1 to recover heat from the exhaust air 54 to the fresh inlet air 56 before 25 heating 53 and entry into the dryer 50. The model was used to predict the following: * Process and mechanical performance for any plant size, based on using the energy recovered from the dryer exhaust to pre-heat the dryer inlet air. 3 0 e Estimates of manufacturing and installation costs for full-size heat exchangers. " Simple economic analysis which predicts values such as the internal rate of return (IRR) using the spray dryer process as an example. N:\MelJbourne\Cases\Patent\80000-80999\P80210.AU\Specis\Amended Specification.doc 11/02/09 - 13 Assumptions made in the model include: * Typical milk spray dryer with a capacity of 10 tonnes/h of powder requiring 15 18 MW of dryer heat (i.e., thermal energy). Definition: Dryer heat = dryer flow rate x (specific enthalpy exhast - specific enthalpy ined). 5 0 Boiler supplying 35 bar steam (enthalpy of 2,803 kJ/kg) and condensate at 10000 (enthalpy of 419 kJ/kg). * Thermal energy costs of $8.00/GJ (2.88 c/kWh). * Fan energy (required to overcome the pressure drop through the heat exchanger) has been deducted from the thermal energy savings. For the sake 10 of simplicity, the fan energy has been costed at the thermal energy rate. Typically, the fan energy was 8-15% of the thermal energy. * Annual operating hours of 4,500 hours. * Scale-up costs based on detailed costing of a 100 kW pilot-scale module and applying a 6/10 power rule. 15 * Savings of both thermal energy and boiler utilisation were incorporated. The latter is argued on the basis of the reduction in demand for the steam boiler. Take, for example, a 15% recovery and reuse of waste heat. In the case of a new installation this means a 15% smaller boiler is required. In the case of a retro-fit, 15% of the boiler capacity becomes available for other uses such as 20 increasing the capacity on the dryer (if energy supply was the bottleneck) or an additional process. Typically, the boiler utilisation savings amounted to 25-30% of the total (i.e. combined) savings. * Interest on capital was set at 10%. Results and Discussion 25 The graph in Figure 13 uses a format where the X axes are labelled "Inlet Air Temperature Rise (*C)", and the Y axes, labelled "lRR" referring to internal rate of return, show a light reference line at the 40% mark. N:\Melbourne\Casea\Patent\8ooo-80999\PB0210.AU\Specia\Amended Specification.doc 11/02/09 - 14 Energy The first aspect modelled was the impact of energy cost (Figure 13) based on taking inlet air (to the heat exchanger) at 30*C and 30% relative humidity (RH) (absolute 5 humidity of 8.0 g/kg). This is typical of dryers which draw their drying air from inside the dryer building envelope. Three levels of prices were modelled being: e $8/GJ (2003 value) 0 $10/GJ (+25%) * $12/GJ (+50%) 10 The model findings show that as energy costs increase the IRR increases significantly. Inlet Air Conditions 15 The second aspect considered was the impact of inlet air conditions (Figures 14 and 15), based on 2003 energy costs ($8.00/GJ). Three conditions were modelled being: * 3000 and 30% RH (absolute humidity of 8.0 g/kg) " 200C and 60% RH (absolute humidity of 8.8 g/kg) 20 e 100C and 90% RH (absolute humidity of 6.9 g/kg) In summary, changes in inlet air temperatures (and humidities) only had minimal impact on the percentage of dryer heat recovered which overall ranged between 10% and 25%. However, higher inlet air temperatures or greater air temperature rises 25 through the heat exchanger reduced the IRR for the installation. Summary Specification Table 1 shows a summary specification for dryers based on the three inlet air 30 temperature scenarios described above that were produced via the model: N:\Melbourne\Casea\Patent\80000-80999\P0210.AU\Specie\Amended Specification.doc 11/02/09 - 15 Table 1. Dryer specifications for different inlet temperature conditions. Description 30 0 C 20 0 C 10*C 30% RH 60% RH 90% RH Air flow rate (m 3 /h) 250,000 250,000 250,000 Mass flow rate (dry, kg/h) 308,313 296,907 287,485 Inlet air temperature rise 30 35 40 (OC) Thermal heat recovered 2,443 2,948 3,486 (kW) % dryer heat recovered 16 17.9 18.9 Surface area (M 2 ) 3,953 3,690 3,546 Fan energy (kW) 316 316 309 Cost Breakdown 5 The following shows a typical cost breakdown as a percentage of total cost: - Heat Exchanger tower 45-55% " Air handling (fans and ducting) 30-40% * Design and installation 8% * Project management 5% 10 In summary, the model analysis demonstrates that an IRR of greater than 40% is achieved in most scenarios. It should be noted that these analyses were based on 2003 energy costs and that energy costs are expected to continue increasing. 15 EXAMPLE 2 A pilot scale heat exchanger was manufactured and retrofitted into an existing dairy factory, commissioned, trialled and then decommissioned approximately 5 months later. A separate skid-mounted fan drew ambient air through a filter and ducted it to 20 the shell-side of the heat exchanger. A description of the spray dryer process is N:\Melbourne\Cases\Patent\80000-80999\P8021O.AU\Speis\Amended Specification.doc 11/02/09 - 16 included in Example 1. For the purposes of the trial, the heated air was vented to atmosphere. Exhaust air was drawn from the base of the spray dryer exhaust stack via a 150 mm 5 tapping, through an isolating valve, fan and pulse-jet filter unit, before being ducted to the tube-side of the heat exchanger. It should be noted that the spray dryer used in the trial is unusual in that it does not have a bag-house filtration system on the dryer exhaust. Rather, it relies on a cyclone system which means the exhaust flow has a higher particulate loading when compared to modern dryers. It is envisaged that future 10 heat exchanger installations would be located downstream of the bag-house and that no further filtration would be required. A clean-in-place (CIP) facility was incorporated alongside the heat exchanger, consisting of a 50 litre tank, single stage centrifugal pump and a rotary spray head. 15 Cleaning was carried out by inserting the spray head into each tube individually and circulating the cleaning solution, followed by a rinse cycle using cold water. The heat exchanger was finally commissioned following a full CIP of the HEX tube side. 20 The following instrumentation was fitted to the heat exchanger for the purposes of the trial: * 4-channel temperature logger measuring: o T1 - Tube-side inlet (i.e. dryer exhaust) 25 o T2 - Tube-side exhaust (to atmosphere) o T3 - Shell-side inlet (i.e. ambient air) o T4 - Shell-side exhaust (to atmosphere) * An hourmeter on both fan VF drives to measure run time. N:\Melbourne\Cases\Patent\80000-80999\P80210.AU\Specia\Amended Specification.doc 11/02/09 - 17 Separate checks were made of the air temperatures and humidity's of the heat exchanger flows using a Testo hand-held instrument and airflows were determined using a Kurz thermo-anemometer. 5 The exchanger was inspected regularly to empty the powder collection bin on the pulse-jet filter, take swabs (for microbial testing), carry out a CIP process on the tube side of the heat exchanger, and to download the logs of temperatures and running hours. 10 The heat exchanger was finally decommissioned after approximately 5 months operation. Results and Discussion The spray dryer used in the trial typically operates for 10-18 hours per day, as shown 15 in the temperature log in Figure 16. At decommissioning, the heat exchanger had been running a total of 1,419 hours. Thermal Performance 20 The heat exchanger's thermal performance was measured periodically during the trial. In all cases a spreadsheet was used to calculate the heat exchanger's thermal performance based on the measured temperatures and airflows. The trials completed enabled an accurate assessment of the exchanger's thermal performance, and Table 1 shows the data from five runs, along with the average of 25 those runs. 30 N:\Melbourne\Cases\Patent\80000-60999\P8021.AU\Speci\Amended Specification.doc 11/02/09 - 18 Table 1: Heat Exchanger Trial Results Description Run 1 Run 2 Run 3 Run 4 Run 5 Ave. Exhaust in temp. 70.3 71.2 71.6 72.1 72.0 71.4 (T1) Exhaustouttemp, 52.7 53.0 53.5 53.8 54.1 53.4 (T2) '7 Air flowrate (m 3 /s) 0.24 0.24 0.24 0.24 0.24 0.24 .> $ Heat lost (kW) 4.55 4.71 4.67 4.72 4.62 4.65 Ambient in temp (T3) 32.0 32.2 32.3 32.4 32.8 32.3 Ambientouttemp 50.5 51.2 51.4 51.8 52.0 51.4 S(T4) " Air flowrate (m 3 /s) 0.20 0.20 0.20 0.20 0.20 0.20 .C Heat gained (kW) 4.17 4.27 4.29 4.35 4.31 4.28 Overall heat transfer 24.2 24.2 24.6 24.4 24.6 24.5 coefficient On average, 0.37 kW (i.e. 8%) of the energy absorbed from the exhaust stream (tube side) was not transferred to the ambient stream (shell-side). This can be explained by 5 way of heat losses from both the un-insulated headworks at the top of the exchanger and the insulated main body of the exchanger. Surface temperatures on the bulk of the insulated body were ~1*C above ambient; however, at the base of the exchanger, where the tube-side return plenum operates at ~60*C, the surface temperatures were -8 0 C above ambient. The measured losses were consistent with design calculations 10 and, in many applications, improved insulation of the hot surfaces (headworks and base) would give a benefit in excess of the cost. Overall, the exchanger's thermal performance was proven to be very close to design values, with heat transfer coefficients of -25 W/m 2 /oC during the trials. 15 A further trial was undertaken where the tube-side flow rate was kept constant at -0.2 m 3 /s (velocity = -12.5 m/s), while the shell-side airflow was varied from 0.0 to 0.35 m 3 /s (velocity = 0-15 m/s). Figure 17 shows the results of the trial and, as expected, the heat transfer increased proportionately with the shell-side velocity. The maximum 20 heat transfer coefficient of 30 W/m 2 /oC provided a heating power of 7.5 kW. N:\Melbourne\Case\Patent\80000-80999\P0210.AU\Specia\Amended Specification.doc 11/02/09 - 19 The intermittent nature of the dryer operation proved an ideal opportunity to identify any mechanical deficiencies, particularly in relation to expansion and contraction issues. Only one deficiency was identified during the trial being a slight deterioration 5 over time in the bonded joint between the tubes and the top plate. An alternative joint design, based on taking the forces in a shear mode and using a proven cast silicon resin will resolve this deterioration. Other bonded joints such as the lap joint in the tubes showed no discernable wear. 10 Microbial performance was also assessed. Particularly in dairy or food applications the design needs to minimise opportunities for the establishment and growth of microbes, as well as yeast and moulds. A total of four sets of swabs were taken during the trial, all immediately prior to CIP cleaning. The tube-side inlet and outlet transitions (at the top of the heat exchanger) were removed and swabs taken from the inside surfaces of 15 the tubes at both the inlet and outlet ends. The swabs were analysed for coliforms, Aerobic Plate Count (APC) and yeast and moulds. All of the results measured were considered to be close to or below the detection limit and consequently of no significant concern. Some condensation (observed as surface droplets) was evident in the tube-side outlet, which is where the stream would be cooled the most. This 20 condensation caused some 'staining' of the tube-side surfaces, however this was readily removed during the CIP cycle. In summary, the heat exchanger's thermal performance during the trial was broadly consistent with design calculations, typically cooling the exhaust air from 750C to 38"C 25 while heating the fresh air (at 0.2 m 3 /s) from 20 0 C to 420C. The tube-side flow rate was lower than the shell-side flow rate. The heat gained by the shell-side air was typically 5.5 kW and the heat transfer coefficient ranged between 20 and 30 W/m 2 /oC. Further, there were no mechanical or microbial issues of any significance during the trial. 30 Conclusions It should be appreciated from the above description that there is provided an air-to-air shell and tube heat exchanger that provides significant improvements in manufacturing and integration costs. This is achieved through: N:\Melbourne\Cases\Patent\80000-80999\P8021.AU\Specia\Amended Specification.doc 11/02/09 - 20 * Reducing mass by the use of thin walled materials. * Reducing labour by replacing welded assemblies with bonded assemblies. * Packaging the heat exchanger in a tower with all head works located at the top and adjacent to the dryer air handling systems. 5 The trials completed demonstrate the viability of the design including: * Thermal design validated and enhancements identified, including modified insulation systems. e Mechanical design validated and enhancements identified, including modified 10 tube-to-plate connections. * The exchanger does not promote the growth of microbiological and fungal organisms and appears to be relatively easy to clean. It should further be appreciated that the heat exchanger of the present invention may 15 have significant value with potential energy savings of 15-20% which may make a significant contribution to a company's bottom line. Further, the resulting "spare" boiler capacity may provide opportunities to enhance company operations elsewhere while the reductions in CO 2 emissions confer significant environmental benefits. Aspects of the present invention have been described by way of example only and it 20 should be appreciated that modifications and additions may be made thereto without departing from the scope thereof as defined in the appended claims. In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary 25 implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention. 3 0 It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country. N:\Melbourne\Cases\Patent\0000-80999\P8021O.AU\Speci\Amended Specification.doc 11/02/09

Claims (24)

1. A shell and tube heat exchanger to exchange heat energy between two fluids including: 5 a shell having a first and second distal end and a first and second shell chamber partitioned using a longitudinal baffle sealing from the first distal end to prior to the second distal end; at least one opening between the first and second shell chamber located prior to the second distal end; 10 a first and second bank of tubes located within the first and second shell chambers; tube header plates disposed transversely to the shell at either distal end of the shell used to retain the tube banks and divided into two halves by the longitudinal baffle with each half corresponding to each shell chamber; 15 an end chamber linking the first bank of tubes in the first shell chamber with the second bank of tubes in the second shell chamber; at least one first shell opening located adjacent the first distal end of the shell and located such that shell side fluid enters or exits the first opening in a transverse direction to the tube bank in the first shell chamber; 20 at least one second shell opening located adjacent the first distal end of the shell and opposing the first shell opening located such that shell side fluid enters or exits the at least one second opening in a transverse direction to the tube bank in the second shell chamber. 25

2. The heat exchanger as claimed in claim 1 wherein the end chamber linking the first bank of tubes in the first shell chamber with the second bank of tubes in the second shell chamber has a U-shaped cross section.

3. The shell and tube heat exchanger as claimed in claim 1 or claim 2 wherein the two 30 fluids are gas streams wherein the gas is selected from: air, steam, and a combination thereof.

4. The shell and tube heat exchanger as claimed in any one of the above claims wherein the shell is a cuboid shape. 35 N:\Melbourne\Caseo\Patent\80000-80999\P8O21O.AU\Specie\Amended Specification.doc 11/02/09 - 22 5. The shell and tube heat exchanger as claimed in any one of the above claims wherein the first shell opening is a single opening along the width of the first tube bank in the first shell chamber.

5

6. The shell and tube heat exchanger as claimed in any one of the above claims wherein the second shell opening is a single opening along the width of the second tube bank in the second shell chamber.

7. The shell and tube heat exchanger as claimed in any one of the above claims 10 wherein the first and second tube banks have an equivalent heat transfer area.

8. The shell and tube heat exchanger as claimed in any one of the above claims wherein the width, depth and height the first and second tube banks and shell chambers enclosing the tube banks are approximately symmetrical. 15

9. The shell and tube heat exchanger as claimed in any one of the above claims wherein the opening between the first and second shell chamber is a single opening along the width of both the first and second tube banks. 20

10. The shell and tube heat exchanger as claimed in any one of the above claims wherein the tube header sheet seals the shell side from the tube side preventing mixing of shell side fluid with tube side fluid and vice versa.

11. The shell and tube heat exchanger as claimed in claim 10 wherein sealing is 25 achieved by using a sealant wherein the sealant is a viscous material that changes state to become solid, once applied, and prevents the penetration of fluids from one location through a barrier into another.

12. The shell and tube heat exchanger as claimed in claim 10 or claim 11 wherein 30 sealant is applied on both the exterior surface and interior surface of the tube header sheet.

13. The shell and tube heat exchanger as claimed in any one of claims 10 to 12 wherein the tube endings on the exterior of the tube header plate sit proud of the plate N.\Melbourne\Caseo\Patent\80000-80999\PB0210.AU\Specis\Amended Specification.doc 11/02/09 - 23 and sufficient sealant is added in the recessed area around the tubes such that the level of sealant is flush with the tube endings.

14. The shell and tube heat exchanger as claimed in any one of claims 10 to 13 5 wherein sufficient sealant is added to the interior of the tubes to form a layer of sealant between the interior of the plate and around the tubes.

15. The shell and tube heat exchanger as claimed in any one of claims 10 to 14 wherein the sealant is a flowable high temperature silicon sealant. 10

16. The shell and tube heat exchanger as claimed in any one of the above claims wherein the tubes are a thin gauge material rolled to a tube shape.

17. The shell and tube heat exchanger as claimed in claim 16 wherein the rolled tubes 15 are fastened together via a welded joint or a lap joint along the tube seam.

18. The shell and tube heat exchanger as claimed in claim 17 wherein a lap joint is sealed by application of sealant along the seam of the joint. 20

19. The shell and tube heat exchanger as claimed in claim 18 wherein the sealant is applied to both the exterior and interior surface of a tube lap joint seam.

20. The shell and tube heat exchanger as claimed in any one of the above claims in which the tubes are laterally restrained. 25

21. The shell and tube heat exchanger as claimed in any one of the above claims wherein the exchanger includes a mechanism to allow for a differential in thermal expansion between the tube bank and the shell. 30

22. The shell and tube heat exchanger as claimed in any one of the above claims wherein the end chamber is releasably attached to the tube bank.

23. The shell and tube heat exchanger as claimed in any one of the above claims wherein in use, flow of fluid through the heat exchanger is counter-current wherein the N:\Melbourne\Cases\Patent\0000-80999\P80210.AU\Specia\Amended Specification.doc 11/02/09 - 24 shell side fluid enters the shell opening on the side opposing the tube bank into which the tube side fluid enters.

24. A shell and tube heat exchanger substantially as hereinbefore described and with 5 reference to the Examples and Figures. N:\Melbourne\Cases\Patent\OOO-80999\P8021O.AU\Speci\Amended Specification.doc 11/02/09