DE3015736A1 - Heat extraction circuit for waste process water - uses heat pump with cooling stages between steam compressors to reduce corrosion - Google Patents

Abstract

The heat pump which extracts heat from water used in an industrial process, passes the wate through a heat extracted steam passed through two compressor stages (20, 21) with a flash cooler (23) between them. This cooler contains water (24) pumped into it from the coil inside the heat exchanger tank. The temperature of the waste water can be 77 deg.C the cold water through the coil being raised from 21 deg.C to 71 deg.C. The extracted steam at 71 deg.C and .035 bar. pressure (absolute) leaves the first compressor at 304 deg.C and 1.75 bar pressure and leaves the flash cooler at 115 deg. C at the same pressure. This cooling action avoids corrosion problems in the circuit. Further cooling stages can be included where further compressor stages are used.

Description

description

There are very large amounts of thermal energy available in liquid flows that have a low heat content, such as the warm emissions from various industrial processes and geothermal currents. The application from heat pumps with a closed circuit to the aforementioned heat sources is in the article "The Heat Pump for Industrial Processes - An Overview "by R. W. Szymanowski (Energy Conservation: A National Forum, Fort Lauderdale, Florida, December 1-3, 1975) and the use of a heat pump with an open circuit is in the essay "Geothermal Powered Heat Pumps to Produce Heat" by D. T. Neill and W. P. Jensen (11th report of the Intercociety Energy Conservation Engineering Conference, September 1976). The one closed circuit having heat pump system has a separate working medium circuit, the heat through a Heat exchanger is transferred to this working medium. In the open circuit system according to the Neill article, will the evaporator heat exchanger is eliminated, and the main source of heat for the working medium circuit consists in the supply of a new one geothermal steam. However, the compressed steam leaving the compressor delivers its heat to a process stream the usual condenser heat exchanger.

The invention is not directed to the generation of process steam per se from liquid flows with a low heat content limited, but the production of process steam is in itself a predominant use of energy in countries such as the United States of America. In 1972 the production of process steam amounted to over 17% of the total energy use in this country. Thus, in a contribution to the recovery of waste heat in liquid streams with Low heat content is seen significant savings in fossil fuels and at the same time the amount of heated water scaled down, passed through cooling towers or to the environment

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is returned.

One of the problems to which the invention is directed is that

The fact that many fluids, such as heads of water steam, can be superheated to a very / degree during compression. Such overheating has an unnecessary increase the power required for compaction and also requires specially designed facilities to make this unnecessary to cope with high temperature. According to a main feature of the invention, there is superheating that occurs during vapor compression occurs in a controlled manner and this also reduces the heat pump installation and the operating costs are simplified or reduced.

One of the main advantages of using an open circuit having heat pumps is the fact that the heat exchangers (condenser and evaporator), which are in common heat pumps are used with closed circuit can be eliminated with the consequence that the temperature drops in such Heat exchangers no longer occur. It is therefore to be expected that improved efficiencies can be achieved.

The term "liquid base" as used herein in connection with low caloric liquid flows is used, refers to their predominant liquid content, such as water in a waste water flow that Contains carried or dissolved liquids, solids or gases. It is the fluid base that the working fluid for forms the open circuit heat pump.

The term "clean" as used herein in relation to the intermediate liquid coolant is used indicates that the incoming liquid intermediate coolant is essentially free of contaminants that with the direct use of the compressed high temperature steam as a process stream is not are compatible.

According to the invention is a having a low heat content Liquid flow partially into a low pressure vapor

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converted, which is compressed to increase its temperature and pressure in several stages. A clean intercooler fluid that is the same as the fluid base of the low calorific fluid flow, is brought into direct contact (e.g. by spraying the liquid) with compressed superheated steam, which through at least one intermediate stage in the various compression stages in a flash vaporizer outside the compression device is generated to the overheating lower this steam and add intermediate coolant steam. The introduction of intermediate cooling liquid into the The flash evaporator is controlled by the fact that the level of the liquid in the flash evaporator is sampled and this level is held in a preselected area. The combined steam flow is further compressed into one flow with a preselected temperature and preselected pressure converted for a direct use as a process troni are suitable. The temperature of the intermediate cooling liquid is preferably increased (if it is not immediately at a desired temperature Temperature is available) by heat exchange with any higher temperature waste heat source, which is available in an appropriate manner. When carrying out the method according to the invention with more than two compressor stages can have many intercooling chambers (i.e. blast chillers) providing direct contact in corresponding Be connected in a way that allows for parallel intercooling, series intercooling or mixed parallel cooling. and to provide intercooling, which depends on the balance between the operational efficiency and the plant costs.

According to the invention, more than one waste heat flow can be used if these are available at one location. These waste heat flows are used in heat exchange relation with the intermediate coolant and / or as a source of steam, which is condensed at the beginning. In those cases in which the intermediate cooling liquid is at a higher temperature

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Is available as the saturation temperature of the steam in For a given intercooler, the intercoolant enters the given intercooler as a liquid / vapor mixture a. The liquid intermediate coolant in such a flow that after direct contact with the compressed Steam is still present, is in turn injected into another intercooler, the one with the given intercooler connected in series, provided the incoming steam is compressed to a lower compression level.

The invention will now be based on further features and advantages the following description and drawing of exemplary embodiments explained in more detail.

Figure 1 is a schematic representation of a flow diagram of the process, intercooling on a Intermediate stage of vapor compression used.

Figure 2 is a schematic representation of a flow diagram of the process shown in Figure 1 with an intermediate cooling at several compression stages by the Use of a parallel line of the intermediate coolant.

Figure 3 is a schematic representation of a flow diagram the process according to the invention, in which the intermediate cooling at several compression stages in one Series routing of the intermediate coolant takes place.

In Figure 1 occurs a liquid flow with a low heat content, which preferably has a temperature of at least 38 C (100 F) has (for example, waste water from an industrial process) into the heat exchanger 11 via a pipe 12, where it transfers thermal energy to a flow of clean intermediate coolant entering through conduit 13. The efficiency of this process can be increased by including this step of heating the intermediate coolant

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because with an intermediate coolant at a higher temperature, larger amounts of intermediate coolant are in the compressed steam can be introduced, and this improves the efficiency due to the increased throughput.

The liquid stream, which has a small heat content, leaves the heat exchanger 11, flows through the line 14 and after a passage through a regulator valve 16 which causes an expansion to the low pressure caused by the pump 17, it enters the expansion chamber 18. In the expansion chamber 18, the two-phase mixture of liquid and steam is separated by gravity as a result of the throttle valve expansion.

The liquid is removed from the chamber 18 by the pump 17 at a predetermined rate and at the same time Time, the steam is removed from the upper part of this chamber via a line 19 by the pumping action of the compressor 20, this vapor being compressed. The compression of the steam not only increases its pressure, but also superheats at the same time Time the steam.

When using an open circuit having heat pumps To achieve significant temperature increases in steam, the compressed steam can be superheated to a temperature which is much higher than the saturation temperature for the resulting pressure. This creates unnecessary enlargement the compression work and also promotes corrosion problems which are volatile in connection with air or other Media occur that can be present in the outflow and are sprayed in together with the water vapor. According to the In the present invention, this disadvantageous overheating is effectively reduced or eliminated by rapid intercooling between successive compression stages. By intermediate cooling according to the invention, the temperatures limited to values that allow the use of cheap or common construction materials.

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Intercooling as a general thought is in heat pump cycles has been used for various purposes. So is the use of intercoolers to reduce compressor work in the above-mentioned article by Neill (page 803, page 2), but the discussion in relation to the recovery the intercooling heat shows that these intercoolers are actually conventional heat exchangers through which the superheated steam in heat exchange with, but separately from, a heat-absorbing process stream flows through it. The usage a flash cooler with vapor compression in a heat exchanger comprising many stages closed loop is in the article "Application of Thermodynamics" by Bernard D. Wood (Addison-Wesley Publishing Co., 1969, pages 186-188. Certain commercially available Water vapor compressors have measures for injecting liquids in intermediate stages and are also suitable for small ones Amount of excess liquid at the inlet to each stage. The liquid injected in this way is therefore a form of Rapid or spray intercooling.

However, the invention is directed to those cases where liquid injection at intermediate stages is impractical, such as for protection against liquid droplet entrapment or flooding, or when liquid separation is required.

Because the intermediate cooling liquid around lower compression levels is performed, the efficiency is increased. Intermediate spray or jet cooling as such it reduces the required compression work by adding both the compression work per mass ton the slight overheating and the mass flow that the lower compression stages have to cope with, since the as an intermediate coolant supplied liquid bypasses the first compression stages (bypass), but part of the final product flow will.

External jet or spray intercooler and associated controls in the German patent application filed at the same time

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P (file number of the same applicant: 832O-RD-11794

with the US serial no. 33,177).

So instead of the compressed, superheated output steam from the compressor 20 directly to the next compressor stage in the

Compressor 21 feed, this output -

steam through a line 22 of the jet or spray intermediate chamber 23 supplied and enters this chamber below the level of the heated intermediate cooling liquid 24, whereby the Steam is brought into direct contact with the liquid 24. The pressure of the clean heated intercoolant that leaves the heat exchanger 11 via line 26 is through the Passage through the pump 27 has been increased to a pressure slightly above the pressure of the compressor 20 in the Chamber 23 is entering steam. The direct contact between the compressed vapor from the compressor 20 and the intermediate cooling liquid 24 causes some of the liquid intercoolant to evaporate and reduce or eliminate at the same time the overheating of the compressed steam. In this way, the exiting flow forms the compressed steam over the line 28 the combination of the compressed steam entering the chamber 23 via the line 22 and the steam supplied to it Intercoolant vapor. The combined flow exiting chamber 23 is at saturation temperature or at a slightly higher temperature at the anticipated pressure in the chamber.

It is important to adjust the amount of intercooling liquid 24 in the To control jet or spray chamber 23 at any given time in order to achieve the required evaporation of the intermediate coolant (thereby bringing about the right amount of superheat reduction in the compressed steam.) and still not so much liquid that liquid droplets are transferred in the vapor stream which the chamber 23 with a small or none at all leaves overheating. This control is brought about that the level of the liquid 24 within a predetermined Limits is kept, this liquid level by a regulator 29 and the combined control / valve arrangement 30 from

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is keyed and controlled, which is usually operated pneumatically or electrically. Examples of devices for exercising These functions are the liquid level regulator (catalog number 2500-249) and the control valve assembly (catalog number 667-EC), manufactured by Fisher Controls Co. Marshalltown, Iowa. Thus, the controller 29 senses the level of the liquid between the connections] ^ a and 29b and generates a pneumatic Output to the control valve assembly 30 which is the sensed level in relation to the level difference between is proportional to connections 29a and 29b. The control valve arrangement 30 determines the size of the intermediate cooling flow in response to this signal to the chamber 23 via the feed line 26 and thereby keeps the liquid level between the set Limit values. A baffle 31 reduces the transfer of liquid droplets in the vapor leaving the chamber 23.

The combined flow of steam from chamber 23 enters the Compressor 21 on and is converted from this as a product flow (for example steam in the case of an initially aqueous flow with low heat content) with a preselected temperature and pressure suitable for direct use as a process stream are suitable.

In a system as an embodiment in which twenty MW,. , of process steam (177 C saturation temperature, absolute Pressure 9.5 bar 29,000 kg / hour ) is to be generated from a sewage outflow with a temperature of 77 C. the operating conditions are as follows:

Incoming wastewater 77 C 1.03 bar absolute

25.4 x 10 kg / hour incoming clean intermediate cooling water 21 C 1.03 bar absolute

4000 kg / hour

Water vapor in jet

chamber 18 71 C 0.35 bar absolute

Water vapor to the compressor 20 71 C 0.35 bar absolute

24 900 kg / hour

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compressed steam to the blasting chamber 23 3O4 ° C 1.75 bar absolute

Intermediate cooling water to the blasting chamber 23 71 C

the compressed steam leaving the blasting chamber 23 at 115.5 ° C. 1.75 bar absolute

In Figure 2 is a flow diagram for the distribution of intermediate cooling liquid to several intermediate stages in one parallel arrangement is shown, wherein the liquid flow having a low heat content over the line 12 in the heat exchanger 11 enters, where they heat to the clean Zwischenkühlf supplies liquid which enters the heat exchanger 11 via a line 13. As in the description above is then the liquid flow having a low heat content to an expansion chamber 18 via a Line 14 and a regulator valve 16 passed and leaves the Chamber 18 via a pump 17. The liquid and vapor are separated by gravity in chamber 18 and the vapor leaves the chamber via a line 19 to a first Stage forming compressor 20 and possibly to be compressed in subsequent compression stages, as follows is described.

Intercooling to reduce the overheating of compressed air Steam from each of the compressors 21 and 32 is in Strahlbzw. Spray chambers 23 and 33 carried out, the intermediate cooling liquid is heated in the heat exchanger 11 and compressed by the pump 34. The one leaving the pump 34 via line 36 Intermediate cooling flow is split to both intermediate expansion chambers 23 and 33 via the parallel arrangement shown serve. Thus, part of the flow sent to the expansion chamber 23 flows through the line 37 and a control valve arrangement 30, while the part of the flow provided for the expansion chamber 33 through the line 38 and the second Control valve assembly 30 flows.

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The liquid entering the expansion chambers 23, 33 is distributed or dispersed therein in order to bring about liquid-vapor contact to maximize by spray nozzles 39 and 41, respectively. Other means, such as perforated plates, guide plates or for example, can also be used wetted walls, used to distribute the liquid. Liquid that is passed down through the chambers 23,33 without evaporating, collects at the bottom, as shown at 24 and 42, respectively.

The control of the admission of intermediate cooling liquid into the Chambers 23, 33 via the control valve assemblies 30, 30 takes place as a function of signals from the liquid level regulator 29, which is connected in the same way as described above in connection with FIG.

With this structure overheating can occur in the compacted Steam leaving the compressor 20 and entering the jet or expansion chamber 23 is reduced to a predetermined level and also the overheating in the steam that

in '

denser 21 and / or the blasting or expansion chamber 33 occurs, can be decreased by a predetermined amount and an even greater flow rate of refrigerant (i.e. working fluid) can be be realized in order to increase the efficiency of the operation.

Thus, working medium in the form of steam, which is compressed on the first compressor stage, enters the jet or expansion chamber 2 3, and the superheating it contains converts the liquid intermediate coolant it contains into vapor around. A combined and therefore increased mass flow of steam enters the next compressor stage in the compressor 21. The one at a higher pressure and a renewed overheating Exposed vapor leaves the compressor 21 to enter a jet or expansion chamber 33 for a second reduction overheating to occur. In the chamber 33 reinforced additional Intermediate coolant vapor that results from the evaporation of distributed liquid due to overheating in the flow inlet

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output of compressed steam is generated from the compressor 21, the incoming compressed steam flow from the compressor 21 and exits compressor 32 as an increased mass flow. The output flow from compressor 32 is the process flow which is produced with the right pressure and the right temperature.

Intermediate cooling at several intermediate stages is also shown in the flow diagram according to FIG. In contrast to In the flow diagram according to FIG. 2, however, the stages for the intermediate cooling are arranged in series one behind the other.

A liquid flow with low heat content is used, in order to generate the working medium in the same way as was described in connection with FIGS. 1 and 2. The steam generated in the jet or expansion chamber 18 flows through the line 19 to the inlet of a low-stage Compressor 20. After this vapor has been compressed and superheated in the compressor, it enters via line 22 in the jet or expansion chamber 23 to be mixed there with dispersed liquid and vapor, as above has been described. The intermediate cooling liquid, which enters the system via line 13, is pumped by pump 51 (via the line 52 and a first control valve arrangement 30) and spray nozzles 39 under pressure into the jet or expansion chamber 23 introduced after being heated in the heat exchanger 11 is. Heated, but not vaporized, liquid intermediate coolant 24 collects at the bottom of the chamber 23. This one higher Temperature-having intermediate coolant is pumped by a pump 53 from the chamber 23 via a line 54 to the chamber 33, where it is distributed via spray nozzles 41. The specified operating conditions of the process preferably produce a complete one Evaporation of the intermediate coolant flow entering spray chamber 33 and brings about the correct downsizing the superheating of the compressed, superheated steam emerging from the second stage compressor-21, which was previously has received a unified flow from chamber 23. the

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desired (i.e. correct temperature and pressure) process flow is achieved by compressing the newly merged flow in the compressor 32 forming the third stage generated.

A level control of the intermediate coolant liquid, which collects in the chambers 23 and 33, and the subsequent division of the liquid flow by actuating the respective Control valve assembly 30 is performed in the general manner described in connection with Figure 1,

A preferred method according to the invention has been described above. However, depending on the particular Increase in temperature to which the work equipment is to be exposed, the number, temperature and nature of the waste heat flows, which are available in one place, and changes are made according to the temperature of the intermediate coolant. The plant is simplified and made more economical by using non-exotic, common construction materials.

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Claims (5)

Expectations Process for the recovery of residual heat from a liquid flow with a low heat content, which is brought to a sufficiently low pressure to absorb part of this liquid flow to spray into a low pressure steam, the low pressure steam increasing its temperature and its pressure is compressed in stages, and the product flow from the last compression stage is called a hot process stream is used, characterized in that a clean intermediate coolant is selected whose liquid phase is the same liquid as the liquid base of the minor ones Heat content having liquid flow, the intermediate cooling liquid with the compressed, superheated Steam is brought into direct contact, which is delivered to at least one intermediate stage of the compression stages Ö30045 / 08BÖ at the same time reducing the superheating of the steam and supplying intermediate coolant vapor, the direct contact in a chamber external to that used for compression Device is performed, and the supplied amount of the intermediate cooling liquid to the external Is controlled by sensing the liquid level in the external chamber to determine the level in a chamber to maintain a predetermined range. 2. The method according to claim 1, characterized in that the temperature of the intermediate cooling liquid before a supply to the external chamber is increased by being in a heat exchange relationship with the one small heat content having liquid flow is brought. 3. The method according to claim 1, characterized in that that the liquid flow having a low heat content is a waste water flow with a Temperature in the range of 38-93 ° C (100-2OO ° F), the liquid intermediate coolant is clean water and the product flow is steam. 4. The method according to claim 1, characterized that the "" * sent to the external chamber liquid intermediate coolants at a temperature higher than the saturation temperature of the compressed, superheated steam and the compressed, heated vapor and a mixture of intermediate coolant liquid and intermediate coolant vapor be brought into direct contact. 5. The method according to claim 1, characterized that in the direct contact between the intermediate coolant liquid and the compressed, superheated steam at a given compression stage that Intermediate coolant remaining in the liquid phase is heated to a higher temperature and this to a higher temperature 030045/0860 Temperature having intermediate coolant liquid into one direct contact with compressed, superheated steam at a higher compression stage in a second jet or flash evaporator is brought outside the facility used for compaction. 03QQ45 / 085Q