US2498008A - Concentration control - Google Patents

Description

Feb. 21, 1950 F. w. SCHMITZ CONCENTRATION CONTROL Filed Dec. 26, 1945 Fwd MSM 3M .THM

Patented Feb. 21, '1950 CGNCENTRATION CONTROL Frederick W. Schmitz, Irvington, N. J., assignor to Research Corporation, New York, N. Y., a corporation of New York Application December 26, 1945, Serial No. 637,280

4 Claims.

This invention relates to air conditioning systems, and control means therefor, and to a method for conditioning air. It is particularly concerned with air conditioning systems in which air or other gas to be conditioned is contacted with an extended surface of a hygroscopic solution, prefrably maintained at a predetermined temperature and preferably comprising an aqueous solution of triethylene glycol, calcium chloride or the like. In the removal of moisture from the air, the hydroscopic solution -becomes diluted and must be concentrated for re-use. To effect concentration, the vdilute solution, or a part of it, is passed to a concentrator. The concentrated solution is then preferably cooled and thereafter re-used to dehumidify additional gas.

` A principal object of the invention is to provide asystem of the character described including improved control means to sense changes in the concentration of the hygroscopic solution and to regulate the operation of the concentrator in accordance with such changes.

A further object is to provide a relatively simple and highly reliable device for sensing changes in concentration or measuring the concentration of solutions whose boiling point varies with concentration.

Another object is to provide a process for conditioning air or other gas involving a unique and simple step for effectively controlling concentration of the hygroscopic solution employed.

' An illustrative embodiment of the principles of the invention will be more particularly described with reference to the accompanying drawing in which:

Fig-1 is a diagrammatic representation of an air conditioning system including a control device embodying lthe principles of the invention, and

Fig. 2 is a sectional elevation of a representative embodiment of the control device of the invention.

In the drawing, the air conditioning system shown includes a dehumidier I, a hydroscopic solution heater 2, a concentrator 3 and a control .device 4. The interrelationship of these components, their separate construction and their respective functions will be more fully described hereinafter.

The dehumidifier I typically takes the form of a housingproviding an enclosed chamberl having an air inlet 5, a transverse baille 6 directing the stream of air downwardly over a coil l, uplwardly through spray eliminators 8 and through Youtlet 9` to the space to be conditioned. A suit- 2 able blower or fan I0 is provided for drawing air through the dehumidifle I Over the outside of coil 1, a lm of hygroscopic solution, such as an aqueous solution of v.triethylene glycol, is caused to ow and inside the coll a cooling medium, such as water, is circulated at a predetermined temperature. Hygroscopic solution is sprayed upon the top of the coil from spray heads I I; it flows by gravity down the coil, drops to the bottom of the dehumidifier and is collected in sump I2. Cooling medium is introduced to the coil through conduit I3 and is led away from the coil through another conduit I4.

The hygroscopic solution which collects inthe sump I2 is picked up by a pump I5 anddelivered to the line I6 from `which it is in part recirculated to the spray heads I I through pipe I1 and in part passed to the concentrator through pipe III.

Valves are provided in pipes II and I8 for regulating the amounts of solution to be recirculated and passed to the concentrator.

The concentrator 3 has avcasing I9 providing a Vertical shaft and having an air inlet 20 near the bottom and an air outlet. 2I at the top. A blower or fan 22 sucks air through the shaft from bottom to top.

Inside the shaft there are located three indirect heat exchangers, typically, finned coils. The uppermost, 23, of these is connected between the pipe I8 and the solution heater 2 so that hygroscopic solution from the dehumidifier sump I2 flows inside the coil on its Way to the heater. Coil 23 functions as a condenser for recovering a portion of the triethylene glycol from the air leaving the concentrator and lreturning such portion to the concentrator; it further functions as a preheater for the solution going to the heater 2.

The intermediate coil 24 is a steam coil, inside of which steam is circulated from a source (not shown). Steam is led to the coil in pipe 25 and condensate is conducted away'from the coil in pipe 26. A control valve 21 regulates the admission of steamto the coil; such valve may be of the on-oli or modulating type; it, in turn', is

regulated by the control device 4 in a manner to be more fully explained hereinafter. A spray of hygroscopic solution from spray heads 28 flows over the outside of coil 24 and is heated thereby to the desired concentrating temperature.

The lower` coil 29I is positioned below the air inlet 20 in the sump of the concentrator. Cooling water from the dehumidifier is circulated inside the coil, the-function of which is to cool hot concentrated hygroscopic solutiminy the sump to a temperature approximately equal to the temperature of the dehumidifier.

Between the air inlet and the steam coil 24 is positioned a column of packing 30. The packing may consist of Raschig rings or other extended surface material over which hot hygroscopic solution ows counter-currently to the stream of air rising in the concentrator.

Concentration of the hygroscopic solution takes place principally in the region of the steam coil 24 and packing 30, although some may occur in the spray region above the steam coil. In concentrating aqueous solutions of triethylene glycol, some glycol is carried above the spray region as entrained and vaporized glycol. The condenser coil 23 cools the gas leaving the concentrator and condenses and returns to the concentrator much of the glycol which would otherwise be lost to the system.

On its way to the concentrator from the dehumidifier, the hygroscopio solution to be concentrated, after leaving the condenser coil 23, passes by Way of pipe 3| to the solution heater 2 Where it is circulated in indirect heat exchange relationship with steam and thereby heated nearly to the concentrating temperature. It is then conducted to the spray heads 28 through pipe 32. Steam is led to the heater by pipe 33 and condensate is removed by pipe 34. Concentrated hygroscopic solution ows from the concentrator back to the sump of the dehumidier through return duct 35.

In operation, where air is to be conditioned by dehumidiiicationv `and cooling, its sensible and latent heat are transferred to the hygroscopic solution flowing over the outside of the coil 1 in the dehumidifier I and thence, by indirect heat exchange, to the cooling water circulating through the coil. Moisture is removed from the air by the hygroscopic solution causing dilution of the latter.

If conditioned air of substantially uniform character is to be delivered by the apparatus, the concentration of the hygroscopic solution must be maintained at a substantially constant value. In the apparatus shown, this condition Ais achieved by controlling the operation of the concentrator 3 in accordance with the concentration of the solution being fed to the spray heads II. It will be understood, however, that such control may, if desired, be in accordance either with the concentration of the solution dripping from the bottom of the coil 'I or with that of the solution found in the sump of the dehumidifier. Suitable sampling devices may be employed, in the latter 5f cases, for removing control samples from the bottom of the coil 1 or from the sump I2 of the dehumidier. The control device 4 has an outer casing 36, which is preferably cylindrical in crosssection, and an inner concentric cylindrical casing 31. The space between the outer and inner casings provides a reservoir for a control sarnple of hygroscopic solution which is bled into the reservoir from the main solution 'line I6 through pipe 38. Pipe 38 is equipped with a valve 39 and a metering orice 4t limiting the flow of solution to the` reservoir to a preselected value. The reservoir is providedv with an overflow pipe 4I which maintains the liquid level in the reservoir constant and returns excess solution to the sump I2 of 'the dehumidifier. Such excess solution may be returned to the system at any other convenient point, for example, it may be led `to the concentrator and there mixed with the solution in the sump' of 'the concentrator.

A heater element 42 is positioned in the lower part of the inner casing 31. Preferably this heater element is of the electric resistance type. A temperature-sensitive device 43 is located in the upper part of the inner casing and is op eratively connected by suitable means 44 to the valve 21 controlling the admission of steam to the concentrator. y

A port 45 admits solution from the reservoir to the bottom of the inner casing 31 and discharge ports 46, located near the top of the inner casing, provide for overilow of solution from the central chamber. Suitable insulation 41 surrounds the lower portion of the inner casing for minimizing the transfer of heat from the inner or boiling chamber to the solution sample reservoir.

The capacity of the heater element 42 is so selected that active boiling of the solution in the central chamber can be quickly established and continuously maintained without, however, causing undue heating of the solution in the reservoir. When active boiling has been established; the central chamber acts as a vapor lift continuously circulating an equilibrium mixture of boiling solution and Vapor into contact with the temperature-sensitive element 43. Some of the mixture is discharged through ports 46 while additional solution is added to the boiling chamber through the lower port 45.

It will be seen that the element 43 at all times senses the true boiling point of a control sample of solution continuously being drawn from the body of solution being pumped to the spray heads of the dehumidier. As the solution becomes cli-I luted through absorption of moisture fromfgas being treated, its boiling point decreases to a temperature at which the temperature-sensitive element has been set to turn on or increase the flow of steam through the valve 21. Conversely, as the solution becomes concentrated through action of the concentrator 3, its boiling point rises to a higher temperature at which the temperature-sensitive element has been adjusted to turn 01T or decrease the flow of steam to the concentrator. 'I

In this manner, the limits of control can be selected in practice to maintain the concentration of the solution within narrow bounds. Illustrative of the degree of control which can be achieved, an aqueous solution of triethylene glycol which is in equilibrium with the partial pres? sure of water vapor in air at about 0% relative humidity at '70 F. has the relatively great varia tion in boiling point of 3 F. for the relatively small variation in concentration of about 0.5%.. Similarly, an aqueous solution of triethylene glycol in equilibrium with air at about 25% relative humidity at 70 F. exhibits a variation in boiling point of 2 F. for a variation in concentration of approximately 1.0%. Thus, it is apparent that small changes in concentration of hygroscoplc solution are reflected in relatively large changes in boiling point so that control of concentration in accordance with boiling point results in very satisfactory operation.`

Alternatively to its control of the heat supply to the steam coil 24, or together therewith,'the control device 4 may be arranged to' regulate the heat supply to the solution heater 2','which 'for present purposes, may be considered tobe a part of the concentrator. It may also turn oil? anden', or modulate the fan 22 drawing air through ,the concentrator, and may be considered yto control the heat supply and other conditions in other d types of concentrators, such as vacuum or atmospheric evaporators.

The circuit lill from the temperature-sensitive element may include means for actuating an alarm signal if the temperature falls below a selected point. Preferably, however, an auxiliary element may be placed in the path of the overiiow from the boiling chamber which will serve to actuate a signal indicating boil or no-boil.

It will be evident that the control device can be utilized for the measurement of actual boiling temperatures by connecting to the circuit 44 a suitably calibrated instrument.

In many cases the operation of the dehumidifier of a gas conditioning system at superatmospheric pressure presents many advantages. For example, if air is dehumidined by contact with a hygroscopic solution at a gauge pressure of pounds per square inch and subsequently released into the conditioned space at atmospheric pressure, the hygroscopic solution may be maintained at a substantially lower concentration, thus eliminating a large amount of corrosion and decomposition difculties. Since the expansion of the air results in a drop in its dry bulb temperature, it is possible in such a system to maintain comfort conditions with cooling medium of higher temperature than would otherwise be effective.

The control device and method of the invention are particularly advantageous with such superatmospheric dehumidifying systems. The hygroscopic liquid in the boiling chamber of the concentrating sensing device may be maintained under the same pressure as that of the dehumidifier or the pressure in the sensing device may be atmospheric. In either case, the control element is, of course, set to maintain the hygroscopic solution at a concentration range effective to condition the gas in the dehumidifier to the desired preselected humidity. For example, if the gas in the dehumidiiier is maintained under 15 pounds per square inch gauge pressure, the gas will be in equilibrium at 70 F. and a relative humidity of 30% with a triethylene glycol solution of 77.3% concentration. A solution of such concentration has a boiling point of 230 F. at atmospheric pressure. To provide the same conditions at atmospheric pressure in the dehumidier, the triethylene glycol solution must have a concentration of 91.2% and a boiling point of 256 F. at atmospheric pressure.

I claim:

1. A device for sensing changes in the boiling point of solutions which comprises means providing a generally vertically extending vapor-lift chamber having solution inlet means near its bottom and discharge means near its top, means for feeding solution to said chamber means through said inlet means at a pressure less than the solution head equivalent to the vertical drop between said discharge means and said inlet means, heating means for boiling solution contained in said chamber means, and a temperature-sensitive element mounted in said chamber means in contact with the actively boiling solution.

2. A device for sensing changes in the boiling point of solutions which comprises an outer casing, a substantially vertically extending casing within said outer casing providing a vapor-lift chamber and cooperating with said outer casing to provide a solution reservoir, said inner casing having a solution inlet port near its lower end and a discharge port near its upper end, both of said ports communicating with said reservoir, means for admitting solution to said reservoir, means for maintaining the solution level in said reservoir at a point between said ports, heating means for boiling solution contained in said inner casing, and a temperature-sensitive element mounted in said inner casing in contact with the actively boiling solution.

3. A device for sensing changes in the boiling point of solutions as defined in claim 2 wherein said means for admitting solution to said reservoir includes means limiting the rate of admission to a maximum value.

4. A device for sensing changes in the boiling point of solutions as dened in claim 2 wherein means is provided for at least partially insulating said reservoir against passage of heat from said vapor-lift chamber.

FREDERICK W. SCHMITZ.

REFERENCES CITED The .following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 173,128 Malligand Feb. 8, 1876 507,633 Peck Oct. 3l, 1893 1,747,742 Stein Feb. 18, 1930 2,017,368 Magner Oct. l5, 1935 2,094,342 Bichowsky Sept. 28, 1937 2,199,967 Bichowsky May 7, 1940

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