DE102006052906A1 - Working medium for steam cycle processes - Google Patents

Abstract

Steam cycle process comprising a feedwater pump for generating an elevated pressure in a working medium used in the steam cycle, a heat transfer arrangement for transferring heat and / or waste heat to the working medium so that the working medium is heated from a low temperature level to a higher temperature level, and an expander for expanding the working fluid under working performance, is characterized in that the working medium is a C <SUB> 1 </ SUB> to C <SUB> 4 </ SUB> alcohol or a mixture of water and / or more of these alcohols, and the higher temperature level is above 170 ° C.

Description

Technical area

• (a) eine Speisewasserpumpe zur Erzeugung eines erhöhten Drucks in einem in dem Dampfkreisprozess verwendeten Arbeitsmedium,
• (b) eine Wärmeübertrageranordnung zur Übertragung von Wärme und/oder Abwärme aus auf das Arbeitsmedium, so dass das Arbeitsmedium von einem niedrigeren Temperaturniveau auf ein höheres Temperaturniveau erwärmt wird, und
• (c) einen Expander zum Expandieren des Arbeitsmediums unter Arbeitsleistung,

The invention relates to a steam cycle process containing

• (a) a feedwater pump for generating an elevated pressure in a working medium used in the steam cycle process,
• (B) a heat exchanger assembly for the transfer of heat and / or waste heat from the working medium, so that the working fluid is heated from a lower temperature level to a higher temperature level, and
• (c) an expander for expanding the working fluid under working power,

Such Steam cycle processes serve to generate work from heat energy. The work can be done, for example, on a wave, with the machinery or motor vehicles are driven. But she can also for the generation of electrical energy by means of a generator serve.

State of the art

Under The term "Clausius Rankine steam cycle" is a Circular process known in which an external burner generates heat. The heat is in a heat exchanger on a working medium, usually Water, transfer. The Working fluid is in the circuit with a feedwater pump circulated. In an expander, such as a piston expander, that will Water relaxes. In this case, a shaft is driven. In a condenser condenses the water and is available again for heat absorption.

Usual working media are water or watery Solutions. A Kalina process is a cycle in which the working medium from several components, especially organic components consists. It is important for all circuits that the working medium does not decompose and meets the environmental conditions. These Ambient conditions include the maximum upper and lower limits minimum lower temperature level. Water is not as a working medium for all Environmentally suitable, for example because it is at low temperatures freezes.

Of the Efficiency of a cycle increases with the difference between the upper and the lower temperature level. It is therefore a high one upper and a lower lower temperature level to achieve a high degree of efficiency desirable.

Disclosure of the invention

It is an object of the invention to find a cycle with an alternative working medium that is suitable for other environmental conditions and allows an increase in the efficiency. According to the invention the object is achieved in that the working medium is a C ₁ to C ₄ alcohol and the higher temperature level is above 170 ° C.

The Use of low melting point alcohols allows the Use even at temperatures below 0 ° C, ie below freezing of water. Due to the low evaporation temperature can evaporate with alcohols at comparatively low temperatures, for example in cooling water, be achieved. The use of alcohols or alcohol mixtures even at temperatures above 170 ° creates a special good efficiency of the arrangement. The invention is based on the surprising Recognition that low-chain alcohols are also above 170 ° for the application are sufficiently stable in a steam cycle. So it is possible for example, cooling water heat at light raised cooling water temperature from 110 ° C through Completely absorb evaporation of the working medium. The working medium can still in the exhaust gas to prevailing high exhaust gas temperatures of for example 400 ° C overheated become.

Carnot's efficiency is: η C = 1 - T u / T O with T _o = upper temperature level and T _u = lower temperature level. At an upper temperature level of 170 ° C and a lower temperature level of 110 ° C, the efficiency is 13.5%, with an increase of the upper temperature level to eg 400 ° C, however, 44%. This is a significant increase in efficiency.

Of the Steam cycle process can be a Kalina process, a Clausius Rankine process or any other suitable steam cycle process. Preferably includes the heat exchanger assembly Means for exhaust heat utilization a primary Combustion process. In a further embodiment of the invention the heat exchanger arrangement additionally comprises means to use the waste heat a cooling circuit. The heat exchanger arrangement can also other heat sources to preheat the Use working medium. this makes possible a high process temperature with low fuel requirements.

In a preferred embodiment of the invention, the working fluid with a lubricating tel.

The Working medium can additionally to the alcohol also contain water and / or methylpyridine. water and methylpyridine form an azeotrope with its own vaporization point. Solve in this azeotrope polar and non-polar substances, in particular also lubricants. The use of alcohol and methylpyridine serves among other things to protect against freezing. Alcohol evaporates at a lower temperature than the azeotrope Water / methyl pyridine. It can absorb the cooling water heat in the low temperature range be used. The water / methylpyridine azeotrope has a higher evaporation point and is particularly suitable for absorbing the exhaust heat or other heat sources in the upper temperature range.

Farther For example, a condenser may be provided to condense the working fluid be. Alternatively, the steam cycle is designed as an open process, as is the case for example in the chemical industry can.

From The alcohols used as the working medium are ethanol and still more methanol is preferred than alcohol.

In In one embodiment of the invention, the working fluid is a lubricant added at the condensation temperature of the lubricant above the Steam outlet temperature is. Then the lubricant is with evaporates and condenses in the expansion in the expander first out. The expander can work this way without a separate oil circuit be lubricated.

One Part of the exhaust steam can be conducted into the crankcase of the expander. Then the crank mechanism by the auskondensierende lubricant lubricated. By connecting to the condenser, the remaining lubricant can subsequently returned to the circuit become. Embodiments of the invention are the subject of the dependent claims. One embodiment is explained below with reference to the accompanying drawings.

Brief description of the drawings

1 schematically shows a steam cycle process that works with methanol as the working medium.

2 schematically shows a Kalina process, which works with an ethanol: alcohol mixture as a working medium

Description of the embodiment

In 1 is a common with 10 designated Clausius-Rankine cycle illustrates. The steam cycle process 10 includes an expansion machine 14 and a heat exchanger 12 , The heat exchanger 12 is acted upon by the waste heat of a primary process. Such primary processes can be power plants or vehicles, such as rail vehicles, trucks, ships or other machines that produce waste heat. Alternatively, the heat exchanger is acted upon by the exhaust gas of a specially provided for this purpose external burner. The cycle also includes a feed water pump 16 and a capacitor 18 ,

The heat exchanger 12 is traversed by working medium in the form of methanol or methanol vapor. The methanol is also accompanied by a lubricant. The working fluid is under an increased pressure, which of a pump 16 is produced. The methanol or methanol vapor is an amount of heat Φ _H supplied from the waste heat. As a result, the steam is greatly overheated, ie brought to a high temperature at about 400 ° C and a higher pressure level of about 4 bar. The inner energy increases.

In an expander, for example a piston expander, turbine or the like 14 the methanol vapor is released. The pressure drops back to a lower pressure level. In this relaxation work is released, which can be harnessed via a shaft, for example, to a generator for electrical energy.

The relaxed methanol vapor then becomes a condenser 18 in which it is condensed, so that the methanol is still available for the cycle. In this case, the amount of heat Φ _c is released, which can be used for example for heat purposes. The condensed methanol is returned to the pump 16 fed.

The described cycle is a typical Rankine cycle. The Carnot efficiency (see _above ) is determined by the upper temperature T _o in the heat exchanger 12 and the lower temperature T _u in the condenser 18 certainly.

Before heating, the methanol is liquid and has the temperature T _u . When heated in the heat exchanger, the liquid is first heated and absorbs energy. At the boiling point, the working fluid begins to evaporate. The temperature initially remains constant until the working medium has completely passed into the gaseous state. The now gaseous working fluid is now further heat energy supplied, resulting in a renewed increase in temperature leads. When the temperature T _{o of} the waste heat is reached, no further heat transfer is possible. The pressurized and hot gas is expanded in an expander and in the condenser 18 cooled until completely condensed again at the low temperature.

By The use of methanol makes it possible to use a low evaporation temperature to achieve sufficient pressure.

In 2 an embodiment is shown in which a Kalina-type cyclic process is used. The cycle is integrated, for example, in an engine for passenger cars.

The diesel engine is common with 110 designated. The diesel engine 110 drives a drive shaft 112 at. The operation of a diesel engine is common technique and therefore need not be explained in more detail. In the diesel engine waste heat is generated, on the one hand via a first cooling system 114 respectively. 116 is discharged to cooling water. On the other hand, hot exhaust gas is generated, of which a partial flow to avoid emission via an exhaust gas recirculation 118 the motor is supplied again. This is indicated by a dashed line 120 represents.

The components described so far are known components of a motor drive system. In contrast to conventional drive systems now the cooling circuit 114 respectively. 116 cooled by another circuit. In this cycle is a multi-component solution as working fluid with a pump 128 pumped at an elevated pressure level of about 4 bar. The working fluid in the present case consists of a carrier substance, namely water, is dissolved in the alcohol. The mass ratio of ethanol: water is dependent on the heat flows cooling water-exhaust gas and is in diesel engines in the range of 40:60.

The water-alcohol solution first takes heat from the engine cooling circuit, which is operated at about 110 ° C., via a plate heat exchanger 132 on. In this plate heat exchanger, the first cooling circuit of the internal combustion engine 110 cooled.

The approx. 110 ° C hot cooling water 114 is cooled to about 105 ° C. The working fluid heats up to approximately 110 ° C during this heat transfer. As a result, a large part of the dissolved alcohol is evaporated. The heat absorption of the working fluid is so large due to the evaporation of the alcohol from the working fluid that can be transferred with small volume flows, the entire accumulating waste heat of the cooling system in the working fluid.

In a second heat exchanger now becomes one of the part of the exhaust heat transferred to the working fluid, the one you want End temperature of the working fluid causes. The temperature of the whole Working fluid with both components then reaches about 400 ° C and that entire working medium has evaporated and overheated. A phase separator is not required in contrast to a pure Kalina process.

The gas under a pressure of 15 bar becomes an expansion machine 138 , For example, a rotary piston machine, piston machine, screw machine or a turbine fed and there to a pressure of, for example, 0.5 bar relaxed. The usable work that is released can be used by the wave 112 be supplied. Then the exhaust steam is in the condenser 136 condensed and over the pump 128 returned to the circuit.

It can also solutions used with other and / or other components that are adapted in nature and proportion of the respective heat sources. The goal is to get one as possible good heat transfer and to allow a high absorption of enthalpy of vaporization. The use of ethanol allows a particularly low evaporation temperature and therefore a higher one Efficiency.

Claims (12)

Steam cycle process comprising (a) a feedwater pump for generating an elevated pressure in a working medium used in the steam cycle process, (b) a heat exchanger arrangement for transferring heat and / or waste heat to the working medium so that the working medium is from a lower temperature level to a higher temperature level and (c) an expander for expanding the working fluid under operating conditions, characterized in that (d) the working fluid is a C ₁ to C ₄ alcohol or a mixture of water and / or more of these alcohols; and (e) the higher temperature level is above 170 ° C. Steam cycle process according to claim 1, characterized in that that the steam cycle process is a Kalina-type multi-component process is. Steam cycle process according to claim 1, characterized in that the steam cycle is a Rankine process. Steam cycle process according to one of the preceding claims, characterized in that the heat exchanger arrangement Means for exhaust heat utilization a primary Combustion process includes. Steam cycle process according to one of the preceding claims, characterized in that the heat exchanger arrangement Means for using the waste heat a cooling circuit includes. Steam cycle process according to one of the preceding claims, characterized characterized in that a capacitor is provided for condensing the working medium. Steam cycle process according to one of the preceding claims, characterized in that the working medium is mixed with a lubricant is. Steam cycle process according to one of the preceding claims, characterized characterized in that the working medium in addition to the alcohol also Contains water and / or methylpyridine. Steam cycle process according to claim 7, characterized in that that the condensation temperature of the lubricant above the Steam outlet temperature is. Steam cycle process according to claim 7, characterized in that a part of the exhaust steam can be conducted into the crankcase of the expander. Use of a C ₁ to C ₄ alcohol as a working medium in a steam cycle process according to one of the preceding claims. Use according to claim 11, characterized that the alcohol is ethanol or methanol.