Apparatus and method for weak liquor flow control in aqua-ammonia absorption cycles

#This invention relates to aqua-ammonia absorption cooling and/or heating systems utilizing ammonia refrigerant and aqueous absorbents. Improvements in the efficiencies of such systems includes the use of generator/absorber heat exchange cycles utilizing rich and weak absorption working fluids and/or by separate heat exchange loops referred to as GAX cycles. Descriptions of such systems are found in U.S. Pat. Nos. 4,311,019, 5,024,063, 5,271,235, 5,367,884, Re. 36,684 and R. J. Modahl and F. C. Hayes, “Evaluation of Commercial Advanced Absorption Heat Pump Bread Board,” The Trane Company, pp. 117-125, 1988. Additional improvements are described in co-pending U.S. patent application Ser. Nos. 479,277, filed Jan. 5, 2000 (ROCKYR.099A); 632,037, filed Aug. 3, 2000 (ROCKYR.105A); 632,054, filed Aug. 3, 2000 (ROCKYR.106A); and 709,875, filed Nov. 10, 2000 (ROCKYR.103A). The description of the aforesaid patents and applications are incorporated herein by reference.

#The present invention is directed to further improvement in efficiency of aqua-ammonia absorption systems. The circulation rate of the weak absorption fluid through an aqua-ammonia absorption system is an important factor in proper operation. The weak solution from the bottom end of the generator, also referred to herein as “weak liquor”, has the lowest concentration of ammonia in the absorption cycle, typically between about 2% and about 20% ammonia, depending on operating mode (heating or cooling), operating conditions, and system design parameters. Excess ammonia in weak liquor decreases the amount of refrigerant generated for a given circulation of solution through the absorption cycle. Thus, the circulation rate must be increased to generate the required amount of refrigerant. Increased solution circulation rate increases the required heat input to the generator, and decreases system efficiency. This efficiency degradation is especially pronounced for GAX systems where circulation rate must be sufficiently high to absorb all refrigerant passing through the condenser and evaporator, but low enough for weak liquor to be adequately depleted in ammonia, which is necessary for the solution to absorb ammonia refrigerant. Moreover, in the case of strong-liquor GAX, ammonia depletion is important to allow the GAX section of the absorber to operate at temperatures sufficiently high for heat transfer to the strong liquor, i.e., absorption fluid solution having relatively high ammonia concentration. Weak liquor with excessive ammonia concentration and low bubble-point temperature reduces the amount of heat that can be recovered in the GAX absorber, thereby reducing system efficiency. Active control of weak liquor flow is needed for optimizing efficiency of the system by maintaining ammonia concentration in the weak liquor within a desired range when temperature conditions change or in systems where firing rate is changeable. As used herein, active weak liquor flow control is intended to mean control and adjustment of weak liquor flow in response to changes in the system or operating conditions in contrast to use only of a fixed restriction such as a fixed orifice or capillary tube. Such weak liquor flow control may also be used advantageously with systems having variable speed or multiple speed burners or firing rates. The terms “burner speed” and “firing rates” are used interchangeably herein.

#As described herein, the flow of weak liquor from the bottom of the generator to the absorber is actively controlled using one or more valves, operated or adjusted in response to a condition or property of the weak liquor, for example, temperature, pressure, concentration and/or, in cooperation with operating conditions, temperatures and/or other sensible parameters.

#FIG. 1 is a schematic illustration showing a generator assembly and a valve and temperature-sensing bulb for controlling the flow of weak liquor;

#FIG. 2 is a schematic illustration of an aqua-ammonia absorption cooling system incorporating the valve and temperature-sensing bulb shown in FIG. 1 for controlling weak liquor flow from the generator to the absorber;

#FIG. 3 is a schematic illustration of an aqua-ammonia cooling system showing the use of combined discrete weak liquor flow control and TXV control of refrigerant flow to the evaporator; and

#Weak liquor flow control as described herein may be used with any aqua-ammonia absorption cooling and/or heating system having an absorber assembly, a generator assembly and an absorption fluid loop for directing absorption fluid between said absorber and generator assemblies. Such systems include a condenser, an evaporator and a refrigerant loop including piping for directing refrigerant from the generator assembly to the condenser and from the condenser to the evaporator. The aqua-ammonia absorption apparatus may perform cooling and/or heating functions. The apparatus include chillers, heat pumps, refrigeration equipment, heating-only appliances, and dual-temperature appliances. The latter are a special type of heat pump that is not reversed, and in which both heating and cooling are produced simultaneously for beneficial use. Such apparatus includes conventional aqua-ammonia systems as well as high-efficiency GAX apparatus, disclosed in the aforesaid patents and applications

#In an embodiment illustrated in FIG. 1, a temperature controlled valve 60 is used for controlling the flow of weak liquor from the generator 11 to an absorber (not shown). The valve is controlled by a temperature-sensing bulb 62 charged with a composition that produces pressure responsive to the temperature sensed by the bulb. The temperature-sensing bulb is installed in thermal contact with the weak liquor in the generator or as it passes through piping or heat exchange coils of the generator. Changes in bulb pressure resulting from changes in the pressure of the bulb charge composition, are directed to a moveable member such as a diaphragm or bellows in the valve resulting in opening and closing the valve in response to the pressure changes, or pressure differential between surfaces of the diaphragm. In the apparatus shown in FIG. 1, valve 60 is positioned between pipes 45 and 47 which direct the weak liquor from the bottom of generator 11 to an absorber (not shown). The valve assembly includes a temperature-sensing bulb 62 in thermal contact with weak-liquor pickup tube 68. Valve 60 is opened and closed in response to the temperature sensed by the bulb 62 in pipe 68 which directs the weak liquor from the bottom of the generator to the GHX (generator heat exchange) coil 65 and pipe 45. Alternatively, the bulb may be placed in thermal contact with the bottom of the generator, either on the outside of the shell where it indirectly measures solution temperature at the bottom of the generator, or in direct thermal contact with solution inside the bottom of the generator. The temperature-sensing bulb may be installed at any desirable location, preferably where the ammonia-weak solution is at or near its bubble-point temperature.

#The valve is diaphragm-controlled with one side of the diaphragm exposed to the temperature-sensing bulb pressure and the other side to generator pressure. The valve components shown include inlet port 71, outlet port 72, diaphragm 73, actuator rod 74, valve plug 75, valve chamber 76 and spring 77. The valve 60 is installed so that the inlet port 71 of the valve receives weak liquor from the generator via pipe 45 and communicates with the valve chamber 76 which is exposed to the diaphragm 73, and the outlet port 72 communicates with pipe 47 for directing the weak liquor to the absorber assembly. The valve outlet port 72 is opened and closed in response to the pressure differential between the generator pressure and the temperature-sensing bulb pressure. The valve regulates weak solution flow rate so as to maintain concentration of ammonia in the weak solution within a desired range. The response of the valve depends on valve design parameters including diaphragm diameter, seat diameter, spring force, and bulb charge. Process parameters such as high-side and low-side pressures, i.e., pressures on the two sides of the valve plug, affect performance.