METHOD AND APPARATUS FOR PRODUCING HIGH-TEMPERATURE HIGH-PRESSURE GAS

Abstract: High temperature and high pressure gas is produced by passing the gas from a compressor (1) in a heat exchange relationship (4) with the exhaust gas from an internal combustion engine (2) used to drive the compressor.

Description: The present invention relates to a method and apparatus for producing a high-temperature, high-pressure gas efficiently and economically. High-temperature, high-pressure gases are used in various fields of chemical industry. One example is in the processing of plastics. In the production of nonwoven fabric from polyethylene or polypropylene by melt blow process, a high-temperature, high-pressure air is used to blow out a molten resin and disperse and stretch it into fibers. Since this air is intended to stretch the molten resin emerging from the nozzle orifice, it is required to have a sufficiently high temperature and pressure. However, an air at an excessively high temperature is not only deleterious to the resin but also uneconomical. Also, an air under an excessively high pressure breaks the stretched fibers and wastes energy. For this reason, it is necessary to properly control the temperature and pressure of the high-temperature, high-pressure gas if the melt blow process is to be performed economically under the optimum conditions. Furthermore, high-pressure, high-temperature gases are commonly used for the purging and regeneration of catalysts and absorbents. They are also used for the heating and drying of industrial products. There are many instances where a reaction gas itself undergoes compression and preheating before it is introduced into a reactor. The production of such high-temperature, high-pressure gases involves the adiabatic compression or polytropic compression of a gas by a compressor and the heating of a compressed gas, which has become hot as the result of compression, with a heating furnace or sheath heater. In general, gases rise in temperature upon adiabatic compression or polytropic compression; however, the temperature is too low for the above-mentioned applications, and they need additional heating by a heating furnace or electric heater. It is not desirable to heat the compressed gas emerging from a compressor to a desired temperature by means of a heating furnace; it needs expensive equipment and impairs the safety measure. Heating by a sheath is safe but adds to production cost. Accordingly, it is desirable to provide a method and apparatus for producing a high-temperature, high-pressure gas safely and economically without the above mentioned drawbacks. US-A-2090214 discloses a method for producing a compressed gas at a high temperature, which comprises the steps of driving a compressor by means of an internal combustion engine and passing the gas discharged from said compressor in heat-exchange relationship with the exhaust gas from said internal combustion engine. The objective here is to recover and use the energy contained in high temperature exhaust gases. There is no temperature sensing arrangement which provides a signal for controlling a valve so as to keep the exhaust temperature constant. The present invention derives from findings that it is possible to obtain a high-temperature, high-pressure gas efficiently by using an internal combustion engine as a prime mover for a compressor and utilizing the heat of the exhaust gas by means of a heat exchanger. Thus according to the present invention there is provided a method for producing a compressed gas at a high temperature, which comprises the steps of driving a compressor by means of an internal combustion engine and passing the gas discharged from said compressor in heat-exchange relationship with the exhaust gas from said internal combustion engine characterised in that the method further includes the steps of measuring the temperature of the high-temperature, high pressure gas discharged from the heat exchanger, producing a control signal on the basis of the measured temperature and operating a flow control valve in dependence on said control signal to adjust the relative amount of the exhaust gas or of the compressed gas entering the heat exchanger such as to maintain said compressed gas at a predetermined temperature. Another aspect of the invention provides an apparatus for producing a high-temperature, high-pressure gas which comprises : (a) a compressor (1) (b) an internal combustion engine (2) adapted to drive the compressor (c) a heat exchanger (4) (d) an intermediate pipe (5) for conducting compressor gas discharged from the compressor into the heat exchanger. (e) outlet pipe means (6) for conducting high-pressure gas emerging from the heat exchanger, and (f) an exhaust pipe (7) for conducting the exhaust gas from the internal combustion engine into the heat exchanger (g) the heat exchanger including means for the exhaust gas and compressor gas to pass in heat exchange relationship whereby the exhaust gas heats the compressor gas characterised in that there is provided a means (11) for measuring the temperature of the gas discharged from the heat-exchanger (4) a means for producing a control signal on the basis of the measured temperature; and a flow control valve (9) operable in dependance on the control signal to adjust the relative amount of the exhaust gas or of the compress or gas entering the heat exchanger such as to maintain said compressor gas at a predetermined temperature. Upon adiabatic compression or polytropic compression by a compressor, the compressed gas rises in temperature to some extent. However, there is an instance where the compressed gas emerging from the compressor is not sufficiently high in temperature. The compressed gas can be heated without a special heating energy if the prime mover for the compressor is an internal combustion engine which emits a high-temperature exhaust gas and heat exchange is performed between the compressed gas and the exhaust gas. The present invention provides a method and apparatus for producing a high-temperature, high-pressure gas at 200-500°C and 2-20 kg/cm²G in a stable manner. The compressed gas emerging from a compressor is heated by heat exchange with the exhaust gas emitted from an internal combustion engine to drive the compressor. To obtain the high-temperature gas at 200-500°C according to the present invention, it is necessary that (1) the internal combustion engine should be one which emits an exhaust gas of high temperature and (2) the compressor should generate a compressed gas having as high a temperature as possible. The first condition may be satisfied by using a known internal combustion engine. The one which emits an exhaust gas higher than 300°C, especially 400-500°C, is preferable. A preferred example is a diesel engine. Heating the exhaust gas further is also within the scope of the invention. It is accomplished by, for example, adding a combustion improver to the exhaust gas containing residual air or using a catalyst to remove NO x in the exhaust gas. The second condition is contrary to the requirement for conventional compressors, i.e., it is important to minimize the temperature rise of compressed gas for the reduction of power cost and the increase of compressor efficiency. This is not desirable for the production of a high-temperature, high-pressure gas, whichis the technical subject of the present invention. Nevertheless, the present inventors succeeded in achieving the object of the invention even by using a known compressor. The temperature of compressed gas at the outlet of a compressor is related to the adiabatic efficiency of compression (n ad ) and the polytropic efficiency (n p ) as shown in the following equations. (Refer to "High-pressure Technology Handbook", pp. 347-349, by Asakura Shoten, 1965.) where, T₁ = inlet temperature T₂ = theoretical outlet temperature (adiabatic reversible compression) T₂′ = actual outlet temperature P₁ = inlet pressure (absolute pressure) P₂ = outlet pressure (absolute pressure) k = adiabatic constant (C p /C v ) According to the present invention, the high-temperature, high-pressure gas at 200-500 C is preferably obtained by heat exchange with the exhaust gas from a driving engine in the case of a compressed gas having an adiabatic constant alpha (= C p /C v ) greater than 1.3. Examples of such a gas include air, oxygen, nitrogen, carbon monoxide, hydrogen, and helium, and mixtures of any of these. The inlet temperature is usually at normal temperature; but it is not specifically limited, though preferably it is higher than -5°C. The compression of a gas is preferably performed such that the compressed gas has a pressure of 2 to 20 kg/cm²G. To this end, compression is usually performed in one to two stages, and the compression ratio P₂/P₁ (ratio of absolute pressure) of each stage should preferably be in the range of 3 to 6. In the case of two-stage compression, the compressed gas emerging from the first stage may be cooled prior to recompression because of the limitation in heat resistance of the compressor. This is also within the scope of the invention. According to the present invention, it is possible to use a compressor having an adiabatic efficiency (n ab ) lower than 80%, usually 50-75%. The present invention does not preclude using compressors having an adiabatic efficiency lower than 50%. In the accompanying drawings : Figure 1 is a schematic drawing for producing a high temperature, high pressure gas according to an embodiment of the invention; Figure 2 is a schematic drawing showing an apparatus producing a high temperature, high pressure has according to another embodiment of the invention. A preferred embodiment of the present invention is described with reference to Fig. 1. Compressor 1 is connected to internal combustion engine 2 via a proper driving means. To the entrance of compressor 1 is connected inlet pipe 3, and to the exit of the compressor is connected intermediate pipe 5 to introduce the compressed gas into heat exchanger 4. Intermediate pipe 5 passes through heat exchanger 4 and connects to outlet pipe 6. To internal combustion engine 2 is connected exhaust pipe 7, which passes through heat exchanger 4. In the middle of exhaust pipe 7, there is attached diverting pipe 8. In the middle of diverting pipe 8, there are attached flow control valve 9 and blower 10. Outlet pipe 6 at the downstream of heat exchanger 4 is provided with temperature detector 11. The output signals from temperature detector 11 are sent to flow control valve 9 through line 12. When internal combustion engine 2 runs, compressor 1 is driven, and compressor 1 sucks a gas through inlet pipe 3 and delivers a compressed gas to the intermediate pipe. The compressed gas is hot on account of adiabatic compression or polytropic compression. The compressed gas subsequently enters heat exchanger 4 through which exhaust pipe 7 of internal combustion engine 2 passes. Thus the compressed gas is heated through heat exchange. The heated compressed gas is discharged from outlet pipe 6 for the subsequent processes. The thus obtained high-temperature, high-pressure gas undergoes temperature control so that it has a desired temperature. This is accomplished by the temperature control mechanism consisting of temperature detector 11, diverting pipe 8, and flow control valve 9 of blower 10. Temperature detector 11 detects the temperature of the gas in outlet pipe 6 and transmits a signal to flow control valve 9 through line 12, said signal being based on the difference between the detected temperature and the desired temperature. Flow control valve 9 controls the amount of the exhaust gas passing through diverting pipe 8. If the gas being discharged through output pipe 6 is excessively high in temperature, flow control valve 9 opens more, allowing the exhaust gas to pass more through diverting pipe 8 and consequently reducing the amount of the exhaust gas that passes through heat exchanger 4. As the result, the high-temperature, high-pressure gas being discharged from outlet pipe 6 reduces in temperature. Conversely, if the gas being discharged from outlet pipe 6 is excessively low in temperature, the above-mentioned operation is performed in reverse. In this manner, the high-temperature, high-pressure gas emerging from the outlet pipe is kept at a constant temperature at all times. In this example, compressor 1 preferably is of such a type that produces a compressed gas having a comparatively high temperature. A preferred example is a screw compressor having a compression ratio of 3 to 6. The compressor preferably has an adiabatic efficiency lower than 80%. Compressor 1 may be used in multiple stage depending on the pressure at the outlet. Usually, it is used in a single stage. In such a case, the resulting compressed gas preferably has a pressure of about 2 to 5 kg/cm²G. This pressure is particularly effective for the melt blow process. In the meantime, the compressor may be provided with a pressure controller for an anomalous pressure rise which might occur due to the clogging of outlet pipe 6. An example of such device is formed by providing a recycling passage across inlet pipe 3 and intermediate pipe 5. The recycling passage is provided with a valve which opens when the pressure in intermediate pipe 5 rises anomalously, so that the gas in intermediate pipe 5 is returned to inlet pipe 3. The internal combustion engine should be one which emits a high-temperature exhaust gas. For this reason, a diesel engine is preferable. The temperature of the exhaust gas from a diesel engine is usually from 300 to 500°C, preferably from 400 to 500°C. Heat exchanger 4 may be of any type. A shell-and-tube heat exchanger is preferable. In this case, the exhaust gas from the engine is preferably passed through the tubes which are easy to clean. Flow control valve 9 attached to diverting pipe 8 may be the suction damper valve of blower 10. Blower 10 is used for the effective introduction of the exhaust gas into the diverting pipe. The flow rate in diverting pipe 8 can be adjusted by flow control valve 9 such as suction damper valve, which makes it possible to control the amount of the exhaust gas that is used for heat exchange in the heat exchanger. Thus it is possible to control the temperature of the high-temperature, high-pressure gas emerging from the outlet pipe. Temperature detector 11 to send control signals to flow control valve 9 may be of any type. It calculates the difference between the detected temperature and the desired temperature and issues a control signal to eliminate the difference. Fig. 2 shows another embodiment of the present invention. Like reference numerals designate like parts in both Fig. 1 and Fig. 2. In the apparatus shown in Fig. 2, intermediate pipe 5 is provided with diverting valve 13, to which is connected bypass pipe 14. Bypass pipe 14 bypasses heat exchanger 4 and joins outlet pipe 6. Temperature detector 11 is attached to outlet pipe 6 at the downstream of confluent point 15. Temperature detector 11 is connected to diverter valve 13 via signal line 16. When the gas in the outlet pipe is excessively high in temperature, the control signal from temperature detector 11 is transmitted to diverter valve 13 through signal line 16. The control signal actuates diverter valve 13 so that the flow rate of bypass pipe 14 increases. As a result, the amount of the compressed gas which bypasses heat exchanger 4 and enters the outlet pipe increases and consequently the gas in the outlet pipe reduces in temperature. When the outlet temperature is excessively low, temperature detector 11 transmits reverse signals. Example 1 An apparatus as shown in Fig. 1 was constructed of the following components: Compressor 1: Screw compressor, Model KS25B, made by Kobe Steel, Ltd. Internal combustion engine 2: Diesel engine, Model S6A2-PTA, made by Mitsubishi Heavy Industries, Ltd. Heat exchanger 4: Shell-and-tube heat exchanger (having a heat transfer area of 67 m²) of the type that the exhaust gas passes through the tubes once. The apparatus was run under the following conditions to produce a high-temperature, high-pressure gas from air: Screw compressor, Model KS25B Air intake: 40 Nm³/min Suction: atmospheric pressure, at 20°C Discharge: 3.5 kg/cm²G, at 230°C Shaft power: 258 kW Diesel engine, Model S6A2-PTA Rated horsepower: 410 PS (at 1800 rpm) 320 PS (at 1300 rpm) Adjustment of revolution: 1300-1800 rpm (infinitely variable) Fuel: Fuel Oil A Temperature of exhaust gas: 410°C Flow rate of exhaust gas: 2080 kg/h The temperature of the exhaust gas emerging from heat exchanger 4 was 320°C, and the temperature of the high-temperature, high-pressure air emerging from outlet pipe 6 was 300°C. The pressure of the high-temperature, high-pressure air was 3.5 kg/cm²G, which is approximately equal to the outlet pressure of compressor 1. It is noted that the temperature of the compressed air was raised from 230°C to 300°C as the result of heat exchange with the exhaust gas. Using embodiments of the present invention, it is possible to produce a high-temperature, high-pressure gas economically and safely, because the compressor is driven by an internal combustion engine and the exhaust gas from the internal combustion engine is used to heat the compressed gas through heat exchange. Even in the case where a compressor having a low adiabatic efficiency is employed, it is possible to produce a high-temperature, high-pressure gas efficiently with less energy, because of the effective use of the surplus heat for the heating of the compressed gas and the recovery of heat from the high-temperature exhaust gas of the internal combustion engine to drive the compressor. The method of the invention is a simple and economical one which may be used to produce a high temperature, high-pressure gas at about 200-300°C and 2-5 kg/cm²G. Furthermore, according to the present invention, it is possible to control the temperature of the high-temperature, high-pressure gas by adjusting the flow rate of the exhaust gas in response to the temperature at the outlet pipe or adjusting the flow rate of the compressed gas passing through the heat exchanger. A further aspect of the present invention relates to the use of the method and/or apparatus to produce a high-temperature high-pressure gas such as air which is employed for stretching molten resin eg polyethylene or polypropylene emerging from a nozzle orifice, to disperse and stretch the resin into fibers, in the so-called melt blown process.

Claims: A method for producing a compressed gas at a high temperature, which comprises the steps of driving a compressor by means of an internal combustion engine and passing the gas discharged from said compressor in heat-exchange relationship with the exhaust gas from said internal combustion engine characterised in that the method further includes the steps of measuring the temperature of the high-temperature, high pressure gas discharged from the heat exchanger, producing a control signal on the basis of the measured temperature and operating a flow control valve in dependence on said control signal to adjust the relative amount of the exhaust gas or of the compressed gas entering the heat exchanger such as to maintain said compressed gas at a predetermined temperature. A method for producing a high-temperature, high-pressure gas as claimed in Claim 1, which further comprises diverting the flow of the exhaust gas from the internal combustion engine and controlling the amount of the diverted flow of the exhaust gas according to the monitored value of the temperature, whereby additional exhaust gas enters the heat exchanger when the measured temperature is too low and less exhaust gas enters the heat exchanger when the measured temperature is too high. A method for producing a high-temperature, high pressure gas as claimed in Claim 1 or 2 which further comprises causing a portion of the gas discharged from the compressor to bypass the heat exchanger and join the flow of the high-temperature high-pressure gas discharged from the heat exchanger, measuring the temperature of the joined gas, and controlling the amount of the bypassing gas in response to the measured temperature to maintain the temperature of the joined gas at a predetermined level. A method for producing a high-temperature, high-pressure gas as claimed in any one of the preceding claims, wherein the compression ratio of the or each stage of the compressor is from 3 to 6, the adiabatic efficiency of compression is lower than 80 % and the adiabatic constant k (=C p /C v ) of the gas being compressed is greater than 1.3. A method for producing a high-temperature, high-pressure gas as claimed in any one of the preceding claims, wherein the pressure of the high-temperature, high pressure gas is from 2 to 20 kg/cm²G and/or the temperature of the high-temperature high-pressure gas is from 200 to 500°C. A method for producing a high temperature, high pressure gas as claimed in any of the preceding claims characterised in that the gas is used in a melt-blown process for producing non-woven fabric by subjecting molten polymer resin such as polyethylene or polypropylene emerging from a nozzle orifice to a current of the high temperature, high pressure gas to disperse the resin and stretch it into fibers. An apparatus for producing a high-temperature, high-pressure gas which comprises : (a) a compressor (1) (b) an internal combustion engine (2) adapted to drive the compressor (c) a heat exchanger (4) (d) an intermediate pipe (5) for conducting compressor gas discharged from the compressor into the heat exchanger. (e) outlet pipe means (6) for conducting high-pressure gas emerging from the heat exchanger, and (f) an exhaust pipe (7) for conducting the exhaust gas from the internal combustion engine into the heat exchanger (g) the heat exchanger including means for the exhaust gas and compressor gas to pass in heat exchange relationship whereby the exhaust gas heats the compressor gas characterised in that there is provided a means (11) for measuring the temperature of the gas discharged from the heat-exchanger (4) a means for producing a control signal on the basis of the measured temperature; and a flow control valve (9) operable in dependance on the control signal to adjust the relative amount of the exhaust gas or of the compressed gas entering the heat exchanger such as to maintain said compressor or gas at a predetermined temperature. An apparatus for producing a high-temperature, high-pressure gas as claimed in Claim 7 wherein the compression ratio of the compressor is from 3 to 6 and the adiabatic efficiency is lower than 80 %. An apparatus for producing a high-temperature, high-pressure gas as claimed in claims 7 or 8 wherein the compressor is a screw compressor. An apparatus for producing a high-temperature, high-pressure gas as claimed in any one of the claims 6 to 8 wherein the internal combustion engine is a diesel engine having an exhaust gas temperature of from 300 to 500 °C. An apparatus for producing a high temperature, high pressure gas as claimed in any of claims 7 to 10 characterised in that the apparatus is used in a melt-blown process for producing non-woven fabric by subjecting the molten polymer resin such as polyethylene or polypropylene emerging from a nozzle orifice to a current of the high temperature, high pressure gas produced by the apparatus to disperse the resin and stretch it into fibres.

Inventors: SHIMADA, SHUJI, SUZUKI, MAKOTO, UENO, MINEO
Applicants: TONEN SEKIYUKAGAKU K.K.
Application year: 1987
Main classification: F02G5
IPC codes: F01N5, F04B17, F02G5