WO2003062517A1

WO2003062517A1 - Controlling the drying process in dry-cleaning machines by means of condensate measurements

Info

Publication number: WO2003062517A1
Application number: PCT/IB2003/000135
Authority: WO
Inventors: Gian Vieri Nardini
Original assignee: Gian Vieri Nardini
Priority date: 2002-01-25
Filing date: 2003-01-21
Publication date: 2003-07-31
Also published as: ITAN20020005A1

Abstract

In a machine comprising a system for drying goods wetted by a liquid, in particular in a dry-cleaning machine for cleaning textile goods by means of a volatile and flammable cleaning solvent, that comprises a system for drying said goods, means (MC; MC1) are provided for measuring the absolute concentration (x2) of vapour in the air at the outlet (S2) of the drum, and methods are provided for releasing, by means of a heating coil (C, Cs, Cb) the maximum heating power allowable under the condition that said absolute concentration (x2) is still lower than or equal to a safe concentration, the latter in turn being lower than the so-called 'lower explosion limit' or LEL. The advantage of the invention is that the drying process can be carried out as fast as possible, within the limits set by safety conditions.

Description

CONTROLLING THE DRYING PROCESS IN DRY-CLEANING MACHINES BY MEANS OF CONDENSATE MEASUREMENTS

DESCRIPTION

This invention refers to industrial cleaning machines that use a solvent. Dry-cleaning processes, a misnomer since they indeed use solvents different from water, are used in many branches of industry, from electronics to mechanics, textile and so on, in any case where contact with water may be harmful for the goods to be cleaned. Their most extensive use is found in connection with clothing and apparel. Some decades ago, the only solvent used for dry cleaning was a variety of petrol: this was contained in a basin, wherein the goods to be cleaned were drenched. When lifted from it, the goods were then left in the air until dry. This procedure carried with it an obviously high risk of fire, and, indeed, later on non-flammable solvents, of the class of halogenated organic compounds, became the preferred ones. At the same time, the machinery underwent considerable improvement, and the open basins were replaced by machines comprising a closed. shell, used for both cleaning and drying. These operations take place in a sequence, the former by soaking the goods in a certain amount of liquid solvent, the latter by means of an air stream that is caused to circulate within the same shell, after emptying out the liquid. These machines have become known by the common name of "dry-cleaning machines" and are mostly designed on a common pattern, according to which the goods to be cleaned are contained in a perforated cylindrical container, named "basket", that turns on an axle, while the outer shell comprises at least two main parts, the first one being called "drum", that houses the basket and is periodically filled with solvent, while the other part, named "air circuit", is used for drying the goods that have been cleaned, communication between the drum and the air circuit being provided by two openings or two groups of openings. One of these brings air to the drum, while the other recovers the same air from the drum, after it has taken along, upon each passage, a part of the solvent vapours contained in the air itself. The air circuit comprises at least the following parts: a fan that causes the air to flow in the desired sense, a heat exchanger fed by a cold fluid, that will be named herein "cooling coil", and that is provided with devices for collecting the solvent condensing in it because of the cold temperature, and a second heat exchanger, or "heating coil", fed by a hot fluid, whose purpose is to heat the air before it returns to the drum.

The cooling coil can be cooled by running water, provided it is available in sufficient quantity and at an appropriate temperature, or, more generally, it is the evaporator of a refrigerating system. In the latter case, it is a usual practice to divide the heating coil in two parts, the first part being the condenser of said refrigerating system. The second part of the heating coil is heated separately, by a supply of hot water or steam, or even simply by an electric resistor. Said second part of the heating coil is usually named "additional coil". The operating cycle of a dry cleaning machine usually comprises the following four phases. In the first phase, the goods that have already been cleaned are dischai'ged and another load of goods to be cleaned is charged into the machine; during this phase there is no solvent in the drum, no air flows in the air circuit, the basket is still and communicates with the outside air by means of a port in the drum through which goods are extracted or introduced. In the second, or soaking, phase, after the port has been shut, the solvent is introduced and the basket is caused to turn slowly, in order to move the goods and to facilitate their contact with the solvent, while no air is flowing yet. In the third, or centrifuging, phase, after draining or. pumping the solvent to a collecting tank, and again with no flowing air, the basket rotation is accelerated until the larger part of the solvent, still contained in the goods, is caused to escape by centrifugal force. In the fourth, or drying, phase, the air flow is finally activated and the basket rotation is slowed down, so to improve contact between the goods and the air that flows in the drum wherein the basket is contained.

During recent years, concern has arisen in the public opinion against the use of halogenated solvents, based on some laboratory experiments, where massive drenches of the same solvents, administered under conditions very different from those of dry cleaning, have caused some animals to develop tumours. As a result, many countries have adopted very strict laws and regulations, and there is even a possibility that the use of halogenated solvents may be soon outlawed in some of them.

The industry is thus going back to using solvents based on pure hydrocarbons, that are supposed to be less toxic than halogenated ones, while indeed flammable. In order to mitigate this drawback of flammability, a solution was found in the use of "cuts", i.e., hydrocarbon mixtures, that are less volatile, and thus also less easily flammable, than those used in the past. The solvent that is presently most used for this purpose in the United States of America has a boiling range around 200°C, and is mainly characterised by a Flash Point (as defined by the Italian norm UNI EN 1127-1) of 63 °C. In some European countries, the use is admitted of some solvents that are even more volatile than the latter, their flash point being 56°C. In both cases, at the flash point temperature, the concentration of solvent vapour that there is in the air in equilibrium with the liquid solvent is about 40 grams per cubic metre: this is the concentration that the same Norm defines as the "Lower Explosion Limit", or LEL for short. In order to grant conditions for maximum safety, one should never reach temperatures higher than the Flash Point temperature of the solvent that is actually present; even greater safety can result from providing a certain allowance, however, this also results in a longer time for drying the goods, especially when these are clothes or apparel, since any further progress in the drying process will make it increasingly difficult to evaporate more solvent at a constant air temperature, until the process becomes uneconomic. In order to overcome this limitation, a number of solutions have been proposed with the intent of preventing fires or explosions: to name but a few, introducing nitrogen or other inert gases, exhausting by means of combustion the oxygen initially present in the drum and in the air circuit, extracting part of the air contained in it, so as to create an ambient at a pressure lower than atmospheric and so on; said solutions are generally expensive and carry with them other drawbacks that are well known to the technicians of this branch. More recently, it has become clear that a dangerous condition is not defined so much by the temperature, as by the concentration of the solvent vapour in the air, and that, if this is kept below a given level, the drying process can be operated while granting a safe condition even if the temperature is higher than the Flash Point. Indeed, a project of European Norm, that was agreed upon by representatives of this branch meeting at. Frankfurt in June 2001, states that drying conditions should be considered safe provided there is no point where the solvent vapour concentration in air is higher than 70 percent, of LEL, even if the temperature is higher than that of the Flash Point. Unfortunately, the devices presently available for measuring this concentration are very expensive and not entirely reliable, and their use for controlling a dry cleaning machine is neither economic nor safe. As a result, while testing a dry-cleaning machine, one only checks that the process conditions allowed during the drying process do not cause concentration to exceed 70 percent, of LEL and/or that the air temperature at the drum outlet, that is the section where the vapour concentration in the air is maximum, does not go over a safe temperature, i.e., that which brings with it, but only under saturation conditions, a vapour concentration equal to 70 percent of LEL. The drawbacks of these solutions are obvious: in the former case, during effective operation anomalous working conditions can develop, that could not be identified during the tests, and that can be dangerous because of missing controls; in the latter case, safety is granted but one refrains from operating at the considerably higher temperatures, even higher than the Flash Point, that could be safely accepted in view of the low vapour concentration, especially in the last part of the drying phase, with the advantage of cutting this a lot shorter. It is a purpose of the present invention to show simple and reliable ways and means for measuring the concentration of a vapour in a gas, and in particular for measuring the maximum concentration of the solvent vapour in the drying air in a dry-cleaning machine as above described, using flammable solvents. It is a further purpose of the present invention, for the same dry-cleaning machine, to show a drying method that allows, at least during a major part of the drying phase, the absolute concentration of the solvent vapour in the air leaving the drum to be kept constant. It is still another purpose of the present invention, for the same dry-cleaning machine, to show a drying method that allows, at least during a major part of the drying phase, to use air at the maximum temperature that can be allowed under safe conditions.

These purposes and other more that will become clearer in the following can be attained by measuring the concentration of vapour contained in the air leaving the drum, through means that measure the quantity of vapour that condenses in the cooling coil during the drying phase, and by supplying to the heating coil, at least during an intermediate period of the drying phase, a quantity of heat related to the quantity of vapour contained in the air leaving the drum, such methods and means being specified and characterised in the claims that are an integral part of the following description.

Further purposes, features and advantages of the present invention will appear clearly from the following detailed description, referring to the enclosed drawings, that are meant to be shown as mere non limiting examples, wherein: Fig. 1 shows, in a schematic form of a dry cleaning machine, the flow sheet of the "air circuit" according to the invention.

Fig. 2 shows, in a qualitative form, a diagram of relative and absolute concentrations of a solvent vapour in the drying air, at different air temperatures and under atmospheric pressure. Before going on to explain the invention, it is useful to recall some concepts and definitions concerning the mixture of a condensable vapour and a gas; said concepts and definitions are currently used in the particular case of air conditioning, but their value is very general, so they can be applied to our case of a solvent vapour diluted in air.

One defines the absolute concentration (usually named "x") of a vapour in a given volume of air as the ratio between the weight of vapour contained in that volume and the volume itself; so the concentration "x" has the dimensions of a weight per unit volume (usually grams per cubic metre). Likewise, in an air stream, whatever its flow rate, the concentration x is expressed as the ratio between the weight flow rate of the vapour and the volume flow rate of the air stream and its dimensions are always those of weight per unit volume. At a given pressure, atmospheric pressure in the case of interest, the absolute concentration x, at any temperature, cannot be more than a maximum saturation value "xsat", that grows with temperature along with the vapour pressure; upon reaching it the air is saturated with vapour and cannot absorb any more. One defines the relative concentration (usually named "phi" and expressed as a percentage) as the dimensionless ratio between the absolute concentration "xsat" actually contained in the air and the saturation concentration "xsat". Coming now to describing the invention, one can remark that the section of the air circuit where the concentration of solvent, and also its flow rate, is maximum, resulting in a most dangerous condition, is at the drum outlet, where the air has been loaded with all the solvent it withdraws from the goods that undergo drying. Almost all the solvent entrained by the air is then left back on crossing the cooling coil, where it condenses and is collected in liquid form. After this treatment, the air leaving the cooling coil is saturated with solvent vapour, but its absolute concentration x is much lower than at the inlet, and, above all, it is strictly determined by the vapour pressure that corresponds with the temperature it has reached in that section; so it is sufficient to know the temperature of the air leaving the cooling coil, in order to know its absolute concentration, since the relative concentration is 100 per cent. Anyway, the air flow rate is known either because it is a design constant of the machine, or, if liable to variations during normal or anomalous working of the machine, it can be easily measured by known means, that will also be mentioned in the following. In order to evaluate the maximum solvent concentration along the air circuit, namely at the drum outlet, all one has to find is the solvent flow rate; as already mentioned, upon crossing the cooling coil it is split into two fractions: that which condenses within the coil and that which goes on and back to the drum in the form of vapour that saturates the air leaving the cooling coil. The latter fraction, as explained, is immediately known, as a function of the air temperature upon leaving the cooling coil.

Accordingly, it is sufficient to measure the flow rate of the liquid solvent collected in the cooling coil in order to calculate an accurate value for the solvent vapour concentration in the air in the most dangerous section.

It is indeed current practice already to do a rough check on the solvent condensed in the cooling coil, in order to control the progress of the drying operation, but the instruments used for this check are very simple and inaccurate, they usually comprise a level sensor placed in a channel where the condensate flows. Said check cannot be defined a measurement, because of the very low accuracy of the method, and indeed its only use is to help deciding when and whether the drying process has come to an end: one considers it has, as soon as the level in the channel has become so low that the sensor no longer feels it.

On the contrary, a very simple means has been found, resulting in a much more accurate measurement, such as to allow its use in controlling the air saturation according to the above described method: one has but to collect the condensed liquid in a container, or in a number of containers with appropriate capacity(ies), whose outlet is temporarily closed, and to measure the time required for filling them with a certain quantity of liquid, detected by an appropriate sensor. On dividing the known quantity of condensed liquid collected in the container(s) into^' the time used for the collection, one finds the condensate flow rate, and can immediately derive the concentration in the section under control.

The above can be more immediately and obviously understood, if referred to some particular, but obviously by no means limiting, examples of embodiment.

Fig. 1 shows schematically the air circuit A, in which air circulates in the direction shown by arrows. The figure shows first the essential and known components of the drying circuit, i.e.: the drum B containing the rotating basket G and the goods to be dried O, the tank S, the cooling coil F, the fan V, and the heating group C comprising a first base heating coil Cb and a second additional heating coil Cs. At the end of the soaking phase and during the centrifuging phase, the solvent contained in drum B is drained to tank S by means of a pump (not shown in the figure) or, by force of gravity, by opening a valve Es. While the cooling coil F and the base heating coil Cb can be, respectively, the evaporator and the condenser of one and the same refrigerating system, with the result that the base heating coil Cb would release a heat quantity strictly related to the heat quantity absorbed by cooling coil F, the heating power released by additional heating coil Cs is controlled independently, whatever its source among all known ones, such as steam, hot water or an electric resistor. The fact that there is an additional coil Cs obviously means that the heating power supplied by the first base heating coil Cb is not. sufficient for the drying process, although, on theoretical grounds, the contrary would seem true, and this is caused by heat losses along the air circuit A. All components named hereto belong to the known state of the art anyway. Along the air circuit A there are also shown four sections crossed by air, SI, S2, Sc and S3, respectively at the outlet of heating group C, at the outlet of drum B, within cooling coil F, at the precise section where the solvent vapour in the air reaches saturation and starts condensing, and, lastly, at the outlet of cooling coil F. At said sections, the air temperatures are respectively tl, t2, tc and t3 and its absolute concentrations are xl, x2, xc and x3, where xl=x3 and xc=x2, since vapour is neither absorbed nor released between sections S3 and SI and between sections S2 and Sc. Before showing how, based on the measurement of the flow rate of solvent condensed by cooling coil F, one can calculate the concentration of solvent vapour in the air leaving drum B, and how this makes it possible to use drying air at the maximum temperature allowable under safe conditions, it is useful to explain the diagram of Fig. 2, which is very similar to the psychrometric charts used for the study and treatment of damp air, but refers to mixtures of air and the vapour of a solvent used for dry-cleaning machines. The transformations of an air- vapour mixture that can be represented on this diagram, shown in Fig. 2 in a qualitative form only (not to be used for design calculations), are well known, and are just summarised here. The ordinates of the diagram are the concentration values of the vapour in air "x", and the abscissas are the temperatures "t" of the air itself. Each of the curves traced on the diagram refers to a constant value of relative concentration "phi". On the curve for- phi = 100 percent, every point has an ordinate equal to the absolute concentration that prevails in saturated air in the presence of free liquid solvent at the temperature t of that point. On the other curves with a constant concentration phi < 100 percent, every point has an ordinate equal to the absolute concentration of vapour that, at the temperature of that point, has a relative concentration equal to the percentage number pertaining to that curve. The diagram also shows the Flash Point temperature, tfp, at which the saturated air contains an absolute concentration equal to the LEL, and a safe temperature ts, related to absolute concentration xs, equal to 70 percent of LEL, that is understood to be a safe limit. The diagram also shows two groups of points: 1, 2, c, 3 and 1', 2', c'(identical with 2'), and, again, 3 that refer to possible states of the air at the four crossing sections, respectively SI, S2, Sc and S3 of Fig. 1 at two different stages of the drying phase; the segments that join said groups of points show the state of the air in intermediate stretches of the circuit in both cases. It has already been pointed out that, since the air leaves the cooling coil F in a saturated state, after losing the greater part of its vapour content, the absolute vapour concentration x3 is exactly determined, for each solvent type, by the outlet temperature t3 of cooling coil F. One can remark that the assurance against exceeding the safe concentration limit xs, equal to

- 70 percent of LEL, can be obtained by watching that the air temperature in crossing section S2 is always t2<ts, since this necessarily results in an absolute concentration x2<xs. This is, however, a very inefficient way of controlling the drying phase. If temperature t2 is indeed kept substantially constant and equal to ts, the corresponding absolute concentration x2 will diminish continuously, down to levels much lower than the saturation level xs, owing to the increasing difficulty in evaporating the solvent while the drying process advances; the time required for drying will thus become too long.

As an alternative, however, one can work at any temperature t2 higher than said safe temperature ts, or even higher than tfp, provided the absolute concentration x2 in section S2 is lower than xs = 70 percent of LEL; the figure shows, for example, that safe conditions are granted if the temperature is equal to tfp, provided the relative concentration phi does not exceed 65 percent, or with an even higher temperature t2 if the relative concentration does not exceed 58 percent.

Going back now to Fig. 1, according to a first simple embodiment of the invention, the device for measuring the quantity of condensed vapour, named MC as a whole, comprises a container Ml with a pipe Tc that connects it with the bottom of the cooling coil F (which drains the solvent condensed by said coil F), an air return pipe Rl (that ensures the equilibrium of pressures between said container Ml and cooling coil F), a level sensor LI and finally a valve Ul, on drain pipe Tsc leading to a tank S. In order to measure the quantity of condensate, one starts from a condition in which valve Ul is open and the condensed solvent flows freely through container Ml into tank S while container Ml stays substantially empty, i.e., there is no condensate retained in it. The measurement is done by closing valve Ul until the condensate, after filling container Ml, reaches level sensor LI. Since the volume of container Ml from the level of valve Ul to that of level sensor LI is known and, obviously, the condensate density is also known, by measuring and recording the time span elapsing between closing valve Ul and the filling signal released by level sensor LI, one can immediately calculate the weight of condensate produced in unit time, i.e, the flow rate of solvent condensed during the measuring time span. Successive condensate measurements can be done after valve Ul has been opened for a time long enough to drain container Ml. The capacity of container Ml shall be small enough and, consequently, filling and emptying times short enough to ensure that between two successive measurements the concentration conditions of air leaving drum B do not vary excessively; on the other hand, said capacity shall be large enough that the percentage measuring error of the condensate collected is acceptable, for a given absolute error of level sensor LI. For example, for the most common sizes of dry-cleaning machines, a capacity of about one litre has been found satisfactory for container Ml, resulting in a filling time of about one minute at the beginning of the drying phase.

According to a second embodiment of the invention, since the condensate flow rate diminishes a lot from start to end of the drying phase, one may prefer to provide the alternative device shown as MCI in fig.l, instead of device MC for measuring the quantity of condensed vapour. Instead of a single container Ml, device MCI comprises two containers Ml and M2, of similar design, but very different capacities. Each has an inlet valve, as shown by the figure, respectively El and E2, an air return duct, respectively Rl and R2, a level sensor, respectively LI and L2, an outlet valve, respectively Ul and U2. In this second embodiment of the invention, neither the connection duct between the two containers, nor valve Ec on said connection duct are present, although the figure shows them. In this embodiment, the measuring method for the condensed vapour starts by using the larger capacity container, then uses the smaller one, toward the end of the drying phase.. More precisely, assuming Ml to be the larger capacity container, on starting the drying phase, valve E2 is kept closed, while valves El, Ul and U2 are open (the last one for the only purpose of ensuring that container M2 is constantly drained). The measurement now goes on as previously described, by closing valve Ul and keeping it closed until level sensor LI signals that container Ml has been filled; valve UΪ is then opened long enough for container Ml to be certainly emptied. These measuring cycles are repeated until the filling time, owing to the increasing dryness of the incoming air, becomes excessive according to the previously mentioned evaluation rules. One then takes on to using container M2 for the following measurements, by simply closing valve El, opening valves Ul and E2, and using valve U2 and level sensor L2 as described above. A third embodiment of the invention allows for three capacity values to be used in a sequence for collecting the condensate, while using only two containers Ml and M2, provided their capacities are different. In this case, one must provide the connecting duct bearing valve Ec between containers Ml and M2, and the former should preferably have a capacity equal to two thirds of that required at the start of the drying phase, the latter one third of the same. The series of measurements should be done according to the following method. One starts with valves Ec, El and E2 in the open position. By closing both valves Ul and U2, each time filling is detected by just one sensor, for example sensor LI, the capacity available is equal to the maximum capacity desired, since both containers Ml and M2 are thus filled at once. As soon as the filling time becomes excessive, container M2 is cut out by closing valves Ec and E2, so the measurements now take place with an available capacity, that of container Ml, that is only two thirds of the initial capacity, and the procedure is the same as for the above described embodiments. As soon as the filling time tends again to become excessive, the measurements are taken over by container M2, by opening valve E2, while container Ml is cut out by closing valve El and keeping connecting valve Ec also closed, and level sensor L2 and valve U2 are also activated.

Many other embodiments are of course possible within the invention, by adding other containers to the already mentioned Ml and M2, likely implemented and used either jointly or in alternative, as above described. One can even provide a single container Mx equipped with a number of level sensors Lx ad different, appropriate levels; by choosing to activate any one of said sensors Lx, one can avail oneself of as many known alternative capacities for collecting condensate as there are levels Lx. In summary, calling M any container Ml, M2 or Mx and E its corresponding inlet valve Ell or E2, R. its air return duct, U its outlet valve Ul or U2, and L its level sensor LI, L23 or Lx, the methods for measuring the condensate flow rate described above comprise:

- draining container M used for the measurement, by opening its outlet valve U,

- closing said outlet valve U and keeping it closed until a given level is reached and detected by its corresponding level sensor L,

- recording the time elapsed between closing said outlet valve U and releasing the signal by said level sensor L, while the corresponding inlet valve E, if present, stays open. According to said procedure, the time required for emptying container M cannot be used for doing measurements. In order to substantially avoid any time gap between two successive measurements, one can take advantage from the following improved procedure that comprises:

- opening the outlet valve U for draining container M and at the same time closing inlet valve E, that is necessarily present in this case,

- closing said outlet valve U and opening at the same time the corresponding inlet valve E, so releasing the condensate produced since the previous closure of said valve E, that will join the new condensate now being produced, to be both delivered into container M, until a certain level is reached, as detected by level sensor L,

- recording the time gap between the closure of said valve E and the emission of the signal from said level sensor L. This procedure will avoid any gaps between successive measurements since new condensate to be measured is already being collected while container M is being emptied. This requires,. of course, using a valve El even if a single container Ml is used.

The examples described hereto show simple methods for measuring the condensate flow rate, which rely on measuring the variable time spans, not determined in advance, that are required in order to fill containers Ml or M2 up to a previously determined level. One can also measure the condensate flow rate by measuring variable and not previously determined quantities of condensate within sampling times that are fixed beforehand but that can possibly differ between successive measurements. One can obtain this, for example, by using known devices, most usually electronic ones, that measure the level reached by condensate in a container having a known volume, or electronic weighing of the condensate quantity recovered. Using a number of different sampling time spans, growing longer and longer while the drying phase advances, has the advantage that one can measure each time a sufficient quantity of condensate for the measurement to be accurate.

In summary, according to the invention, the flow rate of the condensate produced by cooling coil F can be measured by using one or a number of containers such as Ml and M2, either jointly or in a sequence, in which, after they have been emptied through a draining valve that is later closed, all the condensate produced by cooling coil F during fixed or variable time spans is collected and measured by weight or volume, and by calculating said flow rate as the ratio between the quantity of condensate collected and the corresponding collection time. In order for the measurements of the condensate quantities collected to be reliable, in all pipes and ducts Tc and Tsc that respectively join the bottom Ff of cooling coil F with contamers Ml and M2 or the like, and said containers with tank S, the inner sections must be wide enough for the condensed solvent to flow through without lingering either in the. bottom Ff, or in said containers Ml and M2, while said valves El, E2, Ul, U2 are open. The term "valve" is understood to mean an appropriate valve of a known type, that can be operated automatically from a distance, such as an electric valve or, more expediently, as used in dry cleaning machines, a pneumatic valve that is operated in turn by an electric valve, through a pneumatic circuit.

As an alternative to the above described means and methods for measuring the condensate flow rate, that are preferred since they look simple and reliable, any other known flow rate meter can be used, by placing it in a duct connecting the bottom Ff of cooling coil F with tank S, provided the measuring range of said meter is wide enough to include the values of condensate flow rate that are produced since the beginning until the end of the drying phase. In this case, the flow rate is measured continuously instead of by sampling in successive time spans.

For the purpose of the invention, one must know the temperature t3 of the air crossing section S3 and it can be useful to know temperatures tl and t2 respectively pertaining to air crossing sections SI and S2. If the cooling coil F is powerful enough and fed with refrigerating fluid at a constant temperature, temperature t3 is roughly known too, since it approaches that of said refrigerating fluid, however, as a general rule, it is preferable to measure it directly by any known and reliable instrument, while temperatures tl and t2 must necessarily undergo direct measurement in order to become known.

The flow rate of the air that flows in the air circuit A during the drying phase depends on the design features of the dry cleaning machine and on the working conditions prescribed for it. One can consider its value, thus determined, reliable enough, or one can prefer to measure it by means of a flow rate meter P. The latter can be, for example, a differential manometer that measures the pressure difference prevailing between upstream and downstream fan V: since the characteristic curve of fan V is known, from said pressure difference one can immediately calculate the air flow rate.

The invention requires, furthermore, appropriate means for data recording and processing, such as, for example, a microprocessor and an appropriate software, in order to calculate all necessary data on the basis of those that are known or measured; in particular, said recording means shall contain all the necessary data pertaining to the solvent used such as the absolute concentration values x corresponding with the relative saturation concentrations phi for each air temperature, within the range of interest. On calling: - "qc" the weight flow rate of vapour condensed by said cooling coil F, known since measured by the means and according to the alternative methods described above

- "Va" the volume air flow rate in the air circuit, known because of the machine design or measured by the means and according to the methods described above

- "qv2" the weight flow rate of vapour crossing section S2, at the outlet of drum B - "qv3" the weight flow rate of vapour crossing section S3, at the outlet of cooling coil F; it turns out: qv2 = (x2*Va) and qv3 = (x3*Va) and it follows: qc = (qv2-qv3) ^' = [(x2-x3)*Va], then x2 = (x3+qc/Va)

Since absolute concentration x3 strictly depends on temperature t3, that is measured and known, one has all the data required for calculating and keeping under control, at short enough time intervals or even continuously, the absolute vapour concentration x2 at the outlet of drum B. As a result, one can supply, during at least part of the drying phase, the air flowing in air circuit A with a heating power that is strictly related to the above calculated absolute vapour concentration values, by controlling the heating group C or, more exactly, the additional heating coil Cs. In order to prevent concentration x2 reaching a dangerous level even before the first time said concentration x2 is measured, it is sufficient that, at the start of the drying phase, the heating power provided, dependent on the type of dry cleaning machine, is such that the outlet temperature t2 is lower than the safe temperature ts; this can be obtained, for example, by simply starting the drying phase with air at ambient temperature. After sampling has started, it is possible to increase the heating power released by heating coils C stepwise, until absolute concentration x2 reaches a level that is close to, but lower than the safe level xs. If the power released is kept constant from now on, the absolute concentration x2 tends to decrease while the drying process advances; as soon as the decrease of said concentration can be considered meaningful, one can increase again the power released and, as a consequence, temperature tl . This procedure can go on until temperature tl reaches the maximum level that can be tolerated without damage by the goods or apparel to be dried. From now on, temperature tl will be no longer increased, while drying will go on until the absolute concentration xl reaches a lower limit, which is considered to mean that the drying process has been accomplished. One should remark that, for the purposes of the invention, the method of controlling the absolute concentration x2 can substantially work even without directly controlling temperatures tl and- 12. Yet, said control, exerted by appropriate sensors or measuring instruments, is desirable for the following reasons: knowing tl is useful in order to make sure that inlet temperature into drum B at the start of the drying phase is not potentially dangerous, in order to control the power released by heating coils C during the whole course of the drying phase and, finally, at the end of said phase, to keep said temperature from reaching a level that may be dangerous for the goods to be dried; knowing t2 is useful on starting the drying phase, in order to prevent its rise beyond level ts before x2 measurements have started. In the following, an example is described in which the invention is applied according to the second embodiment of the device for measuring the quantity of condensed vapour, mentioned above as MCI.

In the example, the drum B is prepared for dry cleaning a charge of 25 kg of clothes. At the start of the drying phase, after centrifuging, the clothes contains about 7 litres of solvent. Containers Ml and M2 are chosen with capacities of 1 litre and ^lλ litre respectively. Since soaking is always done at a temperature lower than the drying range, one starts by heating, by means of coils C, the air blown by fan V, until temperature t2, as read by an appropriate thermometer, reaches the maximum level considered to be absolutely safe, i.e., temperature ts, at which the concentration of solvent vapour in equilibrium with liquid solvent is 70 percent, of LEL. If the solvent used is the variety that has a Flash Point temperature tfp of 63 °C and LEL of 40 grams per cubic metre, ts is 57°C and it corresponds with a safe concentration xs of (40*0,7) = 28 grams/cubic metre. At this point, one shall start measuring the absolute concentration x2. Let us assume that the air temperature on leaving cooling coil F is 25°C, that corresponds with a residual saturation concentration x3 of 3 grams per cubic metre. So the maximum solvent quantity that can condense in the cooling coil is (28 - 3) = 25 grams per cubic metre of air. If the air flow rate is 2000 cubic metres per hour, the maximum acceptable flow rate for condensate qc is (2000*25/1000) = 50 kg/hour. As the density of the solvent used is close to that of water, at this flow rate filling the 1 -litre container will require (60minutes/501itres) = 1,2 minutes.

As soon as the measurement shows a much longer time to be required for filling, for example 2,0 minutes, this means that the air contains much less solvent than the amount required to saturate it, with regard to its temperature: indeed, each cubic metre of air now loses no longer 25, but (25*1,272,0') = 15 grams of solvent that condenses in the cooling coil; the air that leaves the latter still carries with it 3 grams/cubic metre in the form of vapour; summing up, the air leaves the drum with (15 + 3) = 18 grams/cubic metre, that is much less than the safe limit of 28 grams/cubic metre. This means that the conditions of the charge in that moment are much below those that are considered acceptable for safety: one can then apply more heating power and consequently increase the air temperature tl and the absolute solvent concentration x2, until the latter regains the safe limit, in this case 28 grams/cubic metre, and filling 1 litre again requires but 1,2 minutes. While the drying process advances, filling times tend to become longer again and one can still increase temperature tl and the heating power applied, without danger. The amount of power added at each step, or the size of each temperature increase, that is equivalent to the former, should not cause the concentration to exceed the safe limit xs between two successive measurements of absolute concentration x2. The size of said increase is either fixed in the design of each type of dry cleaning machine, or it can be chosen on a scale of several steps, depending on the amount of difference found between the absolute concentration x2 just measured and the safe concentration xs. In any case, the increases shall always be small enough to avoid exceeding the safe limit xs.

One can of course choose a different procedure, comprising, since the start:

- no control on temperature tl, except the condition that it cannot produce, at the drum outlet, a temperature t2 greater than ts,

- no control on temperature t2, - a measurement, since the start, of the absolute concentration x2.

As the drying process advances, the filling times of container Ml become longer and longer, while more and more heating power is applied, because the goods, on becoming drier, tend to release a smaller quantity of solvent vapour. As soon as the filling time reaches two minutes, it is advantageous to take on measurements by the smaller container M2 that, in the example, has VA litre capacity. As soon as filling this container takes two or three minutes,, the drying process can be taken as completed and the goods can be discharged from the machine. According to this example, the drying phase is taken as completed when the condensate flow rate diminishes below 0,25 kg every 2-3 minutes, or below 0,125-0,08 kg/minute; this limiting value can be different for every machine type and/or drying programme. Whenever, during the drying process, the temperature tl tends to increase over a level that the goods can tolerate, this value being no more than 80°-85°C for not very delicate garments or apparel, the heating power should be reduced, even if, for the purposes of the drying process according to the methods of the invention, said power could be increased while still keeping to a safe condition. Measuring temperatures tl, t2, t3 and the air flow rate Va can be obviously desirable in order to detect possible anomalous, especially if dangerous, working conditions. The advantage provided by the invention is obvious: the drying process can be considerably speeded up in comparison with traditional procedures, since it can use much higher air temperatures than at present, even higher than the flash point temperature tfp, while always insuring a very safe operation, but without the complex devices used hereto. One can finally remark that measuring the condensate flow rate produced by cooling coil F is useful as such in order to detect the end of the drying phase, even if no control is required for safety purposes.

Claims

1. A machine provided with a device for drying objects wetted by a liquid, in particular a dry cleaning machine for cleaning clothes and apparel by a volatile cleaning solvent provided with a system for drying said clothes and apparel comprising: - a container for clothes called drum (B),

- an air circuit (A) in which circulating air is blown by a fan (V),

- a system of coils (C, Cb, Cs), heating the air in order to improve drying,

- a cooling coil (F) for condensing the larger part of the vapour that the air takes up from the clothes, - a tank (S) for collecting the cleaning solvent after condensation, characterised

- by the fact that it is provided with means for measuring, either continuously or periodically, the flow rate of solvent that is condensed by said cooling coil (F) at least during a substantial part of the drying phase carried out under normal operating circumstances,

- and by the fact that the cooling coil (F) has a bottom (Ff) that can collect all the vapour that condenses in said cooling coil (F).

2. A machine provided with a drying system according to the previous claim characterised by the fact that said measuring means comprise any known continuous flow rate meter provided said meter has a measuring range wide enough to include the condensate flow rate values that can be found both at the beginning and at the end of the drying phase. •

3. A machine comprising a drying system according to claim 1, characterised by the fact that said measuring means (MC; MCI) comprise - at least one container (M; Ml; Ml, M2; Mx) connected by ducts .respectively with said bottom (Ff) and with said collecting tank (S) for the cleaning solvent,

- interception means (E; El; El, E2; U; Ul; Ul, U2) such as valves, that can either intercept or open said ducts (Tc, Tsc) in order to effect

- collection, in said one or several containers (M; Ml; Ml, M2; Mx) of all the quantity of solvent that condenses in said cooling coil (F) during specific time intervals,

- and emptying said one or several containers (M; Ml; Ml, M2; Mx) and said bottom (Ff) of the cooling coil (F), air return ducts (R, Rl, R2) such as to always maintain pressure equilibrium between said containers (M; Ml ; Ml, M2; Mx) and said cooling coil (F),

- means capable of measuring, by volume or weight, said quantity of condensate, - calculation means, in particular a microprocessor provided with sufficient means for memory and calculation and an appropriate software,

- means comprising, indifferently

- either memory means containing the pre-established value or values of said specific time intervals, - and/or means for measuring said specific time intervals for which every measurement can report a different value, said means being able to supply said calculation means with the measured values of said specific time intervals, all said means being able, together, to carry out the calculation of the weight flow rate of condensed solvent that is produced by cooling coil (F) in said time intervals, as the ratio between said quantities of condensed solvent and the corresponding time intervals, after multiplying said condensate quantity, if measured by volume, by the known specific weight of said condensate, while the inner sections of said ducts (Tc, Tsc) and said interception means (E; El; El, E2; U; Ul; Ul, U2) are ample enough to allow the condensed solvent to flow easily and quickly, without lingering in the bottom (Ff), nor in said containers (M; Ml; Ml, M2;

Mx) when said interception means (E; El; El, E2; U; Ul; Ul, U2) are open.

4. A machine comprising a drying system accordmg to the previous claim characterised by the fact that said means capable of measuring said condensate quantity

- comprise a known device, generally an electronic one, that can measure all the weight quantity of condensate produced by said cooling coil (F) during every one of said time intervals and fully collected in said one or several container(s) (M; Ml; Ml, M2; Mx),

- while said means that can supply the value of said specific time intervals comprise memory means containing the pre-established value or values of said time intervals.

5. A machine comprising a drying system according to claim 3, characterised by the fact that said means capable of measuring said condensate quantity comprise a known device, generally an electronic one, that can measure all the volume quantity of condensate produced by said cooling coil (F) during every one of said time intervals and fully collected in said one or several containers (M; Ml; Ml, M2; Mx),

6. A machine comprising a drying system according to claim 3, characterised by the fact that said means capable of measuring said condensate quantity comprise

- one or several level sensor(s) (L; LI; LI, L2; Lx) that can detect said pre-established levels being reached within said one or several container(s) (M; Ml; Ml, M2; Mx) in which all the condensate quantity produced by said cooling coil (F) during every one of said time intervals is fully collected,

- being the volumes corresponding to said pre-established levels fixed and known for every one of said one or several container(s) (M; Ml; Ml, M2; Mx),

- while said means for supplying the value of said specific time intervals comprise means for measuring said specific time intervals.

7. A machine comprising a drying system according to the previous claim characterised by the fact that said condensate quantity is that collected within said one or several container(s) (M; Ml;

Ml, M2; Mx) since the moment when the corresponding outlet valve (U; Ul; Ul, U2) is closed until the moment when the signal arrives from the corresponding level sensor (L; LI; LI, L2; Lx) while the bottom (Ff) of the cooling coil (F) is allowed to continuously drain towards said one or several container(s) (M; Ml; Ml, M2; Mx),

- being possible to proceed with a successive flow rate measurement only after that said outlet valve (U; Ul; Ul, U2) is kept open again for a time sufficient to allow the drainig of said one or several containers (M; Ml; Ml, M2; Mx).

8. A machine comprising a drying system according to claim 6, characterised by the fact that said condensate quantity comprises

- that first portion that is produced by cooling coil (F) and collects in its bottom (Ff) while the outlet valve(s) (U; Ul; Ul, U2) of said one or several container(s) (M; Ml; Ml, M2; Mx) used for collection is kept open for draining of one or several container(s) (M; Ml; Ml, M2; Mx) and, at the same time, a corresponding interception means, comprising an inlet valve (E; El ; El, E2) is kept closed, - plus that second portion that

- having finished draining said one or several container(s) (M; Ml; Ml, M2; Mx),

- having closed the corresponding outlet valve(s) (U; Ul; Ul, U2),

- and opened the corresponding inlet valve (E; El; El, E2) for draining said bottom (Ff), - continues being produced by cooling coil (F) and is channelled into said one or several container(s) along with said first portion until the level has been reached that is detected by the corresponding level sensor (L; LI; LI, L2; Lx), it being possible to immediately proceed with a successive flow rate measurement, as soon as said outlet valve (U; Ul; Ul, U2) is opened again, after said level has been reached, as detected by said corresponding level sensor (L; LI; LI, L2; Lx), while, at the same time, the corresponding inlet valve (E; El; El, E2) is kept closed again.

9. A machine comprising a drying system according to any one claim from 3 to 7, characterised by the fact that for measuring said condensate quantities produced in said time intervals a measuring means (MC) is provided that comprises a single container (M; Ml) with a corresponding outlet valve (U; Ul) and a corresponding level sensor(L; LI)

10. A machine comprising a drying system according to claims 8 and 9, characterised by the fact that for measuring said condensate quantities produced in corresponding time intervals, said container ( M; Ml) is also provided with a corresponding inlet valve (E; El).

11. A machine comprising a drying system according to any one claim from 3 to 8, characterised by the fact that for measuring said condensate quantities produced in corresponding time intervals, a measuring means (MCI) is provided, that includes at least two containers (Ml, M2), each having a corresponding outlet valve (Ul, U2) and a corresponding inlet valve (El, E2), being said containers (Ml, M2),

- different in their capacities,

- and capable of being used separately for measuring said condensate quantities by simply keeping closed the inlet valve (El, E2) that corresponds to any container that is not being used.

12. A machine comprising a drying system according to the previous claim characterised by the fact that . two; or several of said containers (Ml, M2) can also be used jointly, by opening connection valves (Ec) that connect all and only those containers that are to be used jointly.

13. A machine comprising a drying system according to any one claim from 3 to 8, characterised by the fact that the means for measuring said condensate quantities produced in corresponding time intervals comprise a container (Mx) provided with two or more level sensors (Lx), every one of which corresponds to a different level and to a different known capacity of said container (Mx).

14. A machine comprising a drying system according to claim 11, characterised by the fact that it comprises a first container (Ml) with a capacity of 1 litre and a second container (M2) with a capacity of % litre.

15. A machine comprising a drying system according to claim 12, characterised by the fact that it comprises a first container (Ml) with a capacity that is twice the capacity of a second container (M2).

16. A machine containing a system for drying objects wetted with a liquid, in particular a dry- cleaning machine for cleaning clothes by means of a volatile cleaning solvent, and provided with a system for drying said clothes comprising

- a container for clothes called drum (B),

- an air circuit (A) wherein air is circulated by a fan (V),

- an air heating coil (C, Cb, Cs), to make drying easier,

- a cooling coil (F) for condensing the larger part of the vapour that the air has driven from the clothes,

- a tank (S) for collecting the cleaning solvent that has condensed, characterised by the fact that it is provided with means for measuring, either continuously or intermittently, and during a substantial part of the drying phase carried out during normal working conditions, the absolute concentration (x2) of solvent vapours at the section (S2) between the outlet from drum

(B) and the inlet into the cooling coil (F).

17. A machine comprising a drying system according to claim 16, characterised by the fact that said means for measuring said absolute concentration (x2) comprise

- means for measuring the weight flow rate (qc) of solvent condensed by said cooling coil (F),

- calculating means, in particular a microprocessor with sufficient calculating and memory means, and an appropriate software capable of

- giving the absolute concentration (x3) corresponding to temperature (t3) in said section (S3) at the outlet of cooling coil (F), - calculating said absolute concentration (x2), based on the knowledge of said weight flow rate (qc), said absolute concentration (x3) and the volume flow rate (Va) of air that circulates in the air circuit (A), wherein said volume flow rate of air (V) is

- either known and memorised in said memory means, - or measured by an appropriate flow rate meter (P), and wherein also said temperature (t3) is

- either known and memorised in appropriate memory means,

- or measured by an appropriate meter.

18. A machine comprising a drying system according to claim 17, characterised by the fact that means are provided for measuring the weight flow rate (qc) of solvent condensed by said cooling coil (F), such as characterised in any one or several claims from 1 to 15..

19. A machine comprising a drying system according to any of the previous claims, characterised by the fact that means are also provided for measuring the air temperature (tl) in the air crossing section

(SI) at the inlet of drum (B) and/or for measuring the air temperature (t2) in the air crossing section (S2) at the outlet of drum (B).

20. In a machine containing a system for drying objects wetted with a liquid, in particular a dry-cleaning machine for cleaning clothes by means of a volatile cleaning solvent, and provided with a system for drying said clothes comprising

- a container for clothes called drum (B), - an air circuit (A) wherein air is circulated by a fan (V),

- an air heating coil (C, Cb, Cs), to make drying easier,

- a cooling coil (F) for condensing the larger part of the vapour that the air has driven from the clothes, - a tank (S) for collecting the cleaning solvent that has condensed, a method for ascertaining the absolute concentration (x2) of solvent vapour in the section of maximum concentration, in particular corresponding with the air crossing section (S2) immediately at the outlet of said drum (B), characterised by the fact of

- measuring the flow rate of condensate (qc) produced by said cooling coil (F), - measuring or retrieving from pre-memorised data the temperature (t3) in a section (S3) of the air circuit (A) at the outlet of cooling coil (F), calculating the absolute concentration of vapour (x3) corresponding with said temperature

( 3),

- measuring or retrieving from pre-memorised data the air flow rate (Va) circulating in the air circuit (A),

- calculating said absolute concentration (x2) as a function of said data (qc, x3, Va).

21. A method for ascertaining the absolute concentration (x2) of solvent vapour in the section of maximum concentration, according to the previous claim, characterised by the fact that every measurement of said condensate flow rate (qc) is obtained by - collecting all and only that condensate quantity that is produced by said cooling coil (F) in a corresponding time interval in one or several containers (M; Ml; Ml, M2; Mx), that are empty at the start,

- measuring said condensate quantity,

- dividing said condensate quantity resulting from said measurement into the specific time interval that was required by said cooling coil (F) to produce it

- emptying again said one or several containers (M; Ml; Ml, M2; Mx), at least when it is necessary to proceed with successive flow rate measurements.

22. A method for ascertaining the absolute concentration (x2) of solvent vapour in the section of maximum concentration, according to the previous claim, characterised by the fact that for every measurement of said condensate flow rate (qc)

- said condensate quantities are variable, - while said time intervals are determined beforehand,

- it being possible for said pre-determined time intervals to have more than one different duration, preferably increasing from the start until the end of the drying phase.

23. A method for ascertaining the absolute concentration (x2) of solvent vapour in the section of maximum concentration, according to claim 21 , characterised by the fact that for. every measurement of said condensate flow rate (qc)

- said condensate quantities are variably chosen,

- while said corresponding time intervals are variable and ascertained by measurement.

24. A method for ascertaining the absolute concentration (x2) of solvent vapour in the section of maximum concentration, according to claim 21 , characterised by the fact that for every measurement of said condensate flow rate (qc)

- said condensate quantities are determined beforehand,

25. A method for ascertaining the absolute concentration (x2) of solvent vapour in the section of maximum concentration, according to the previous claim, characterised by the fact that said pre-determined condensate quantities are of several different sizes, decreasing from the start until the end of the drying phase.

26. A method for ascertaining the absolute concentration (x2) of solvent vapour in the section of maximum concentration, according to the previous claim, characterised by the fact that said condensate quantities, decreasing from the start until the end of the drying phase, are chosen one after another in order that the corresponding time intervals for the production of condensate keep within minimum and maximum duration limits that are determined beforehand.

27. A method for ascertaining the absolute concentration (x2) of solvent vapour in the section of maximum concentration, according to the previous claim, characterised by the fact that said pre-determined minimum and maximum duration limits for said time intervals for the production of condensate are respectively equal to 1 and 2 minutes.

28. In a machine containing a system for drying objects wetted with a liquid, in particular a dry-cleaning machine for cleaning clothes by means of a volatile cleaning solvent, and provided with a system for drying said clothes comprising

- an air heating coil (C, Cb, Cs), to make drying easier,

- a cooling coil (F) for condensing the larger part of the vapour that the air has driven from the clothes, - a tank (S) for collecting the cleaning solvent that has condensed, a method for ascertaining that the drying phase has been accomplished, characterised by the fact of

- measuring the condensate flow rate (qc) produced by said cooling coil (F), comparing said resulting flow rate value with a reference limit, - taking the drying phase as being accomplished when said resulting flow rate value is smaller than said reference limit. ^■

29. A method for ascertaining that the drying phase has been accomplished, according to the previous claim, characterised by the fact that said reference limit is within the bracket from 0,08 and 0, 125 kg/minute.

30. A method for ascertaining that the drying phase has been accomplished, according to the previous claims 28 or 29, characterised by the fact that the measurements of said condensate flow rate (qc) are carried out according to any one of the methods characterised by claims from 20 to 28.

31. In a machine containing a system for drying objects wetted with a liquid, in particular a dry-cleaning machine for cleaning clothes by means of a volatile cleaning solvent, and provided with a system for drying said clothes comprising

- a container for clothes called drum (B),

- an air circuit (A) wherein air is circulated by a fan (V),

- an air heating coil (C, Cb, Cs), to make drying easier, - a cooling coil (F) for condensing the larger part of the vapour that the air has driven from the clothes,

- a tank (S) for collecting the cleaning solvent that has condensed, a method for carrying out the drying process characterised by the fact that at least during a part of the drying process, the heating power supplied to the air that enters the drum (B) depends on the value of absolute concentration of vapour (x2) as measured at the outlet of the same drum (B), or, more exactly, the amount of heating power supplied is such as to maintain said absolute vapour concentration (x2) constantly lower than, but as close as possible to a reference value (xs).

32. A method for carrying out the drying process according to the prvious claim, characterised by the fact that starting from a given time, during the drying phase,

(a) a measurement is done of said absolute vapour concentration (x2),

(b) the resulting value is compared with said reference value (xs),

(c) more heating power is supplied if and only if

- said absolute vapour concentration (x2) is lower than said reference value (xs), - it is possible to deliver an increment of heating power small enough to prevent said absolute vapour concentration (x2) exceeding said reference value (xs), the possibility being provided that said steps (a), (b), (c), can be repeated any number of times, while the measurement of said absolute vapour concentration is done according to any one method characterised by claims from 20 to 27. .

33. A method for carrying out the drying process according to the previous claims 31 or 32, characterised by the fact that

- at the start of the drying phase, air is introduced into drum (B) at a temperature (tl) lower than the safe temperature (ts) or anyway such that the temperature (t2) at the outlet of drum (B) is certainly lower than or equal to said safe temperature (ts), - while said steps (a), (b), (c), are done and repeated since the start of the drying phase.

34. A method for carrying out the drying process according to any one of the previous claims from 31 to 33, characterised by the fact that

- upon starting the drying phase, the air is heated progressively, until it reaches at the outlet of drum (B) a temperature (t2) equal to said safe temperature (ts), - a measurement being provided for said temperature (t2),

- while said steps (a), (b), (c), are done and repeated starting when said safe temperature (ts) has been reached.

35. A method for carrying out the drying process according to any one of the previous claims from 31 to 34, characterised by the fact that the control of the heating power delivered by said heating coil (C, Cb, Cs) depends on controlling the temperature (tl) of the air being introduced into drum (B).

36. A method for carrying out the drying process according to any one of the previous claims from 31 to 35, characterised by the fact that the temperature (tl) of the air being introduced into drum (B) is kept lower than a value that is considered to be harmful for the goods being dried.

37. A method for carrying out the drying process according to any one of the previous claims from 31 to 36, characterised by the fact that the safe absolute concentration (xs) is equal to 70 percent of the absolute concentration at the lower explosion limit (LEL) of the solvent in use.

38. A method for carrying out the drying process according to any one or several of the claims

39. A machine containing a system for drying objects wetted with a liquid, in particular a dry- cleaning machine for cleaning clothes by means of a volatile cleaning solvent, and provided with a system for drying said clothes comprising

- an air heating coil (C, Cb, Cs), to make drying easier,

- a tank (S) for collecting the cleaning solvent that has condensed, provided with any one or several systems and means characterised by claims 1 to 19 and capable of carrying out any one or several methods characterised by claims from 20 to 38.