WO2008055720A2

WO2008055720A2 - Working medium for steam circuit process

Info

Publication number: WO2008055720A2
Application number: PCT/EP2007/058873
Authority: WO
Inventors: Michael Hoetger; Jörg COLLISI
Original assignee: Amovis Gmbh
Priority date: 2006-11-08
Filing date: 2007-08-27
Publication date: 2008-05-15
Also published as: DE102006052906A1; WO2008055720A3

Abstract

The invention relates to a steam circuit process comprising a feed-water pump for generating a higher pressure in a working medium used in the steam circuit process, a heat exchanger arrangement for transmitting heat and/or waste heat to the working medium such that the working medium is heated from a lower temperature level to a higher temperature level, and an expander for expanding the working medium with efficiency. The steam circuit process is characterised in that the working medium is a C1 to C4 alcohol or a mixture of water and/or a plurality of said alcohols, and the higher temperature level is above 170°C.

Description

Patent application

AMOVIS GmbH. Voltastraße 5. D - 13355 Berlin Working medium for steam travel processes

Technical area

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 medium of a lower

Temperature level is heated 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 thermal energy. The

For example, work can be done on a shaft that drives machinery or automobiles. But it can also serve to generate electrical energy by means of a generator. State of the art

The term "Clausius-Rankine steam cycle process", a cycle is known in which an external burner generates heat. The heat is transferred in a heat exchanger to a working medium, usually water. The working medium is circulated by a feedwater pump in the circuit. In an expander, such as a piston expander, the water is released. In this case, a shaft is driven. The water condenses in a condenser and is again available for heat absorption.

Common working media are water or aqueous solutions. A Kalina process is a cycle in which the working medium consists of several components, in particular organic components. It is important for all circuits that the working medium does not decompose and meets the ambient conditions. These environmental conditions include the maximum upper and minimum lower

Temperature level. Water is not suitable as a working medium for all environmental conditions, for example because it freezes at low temperatures.

The efficiency of a cycle increases with the difference between the upper and lower temperature levels. It is therefore a high upper and a lower lower one

Temperature level to achieve a high 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 Ci to C ₄ - alcohol and the higher temperature level is above 170 ⁰ C.

The use of low melting point alcohols allows use even at temperatures below 0 ^° C., ie below the freezing point of water. Due to the likewise low evaporation temperature, it is possible with alcohols to achieve evaporation at comparatively low temperatures, for example in cooling water. The use of alcohols or alcohol mixtures even at temperatures above 170 ° thus provides a particularly good efficiency of the arrangement. The invention is based on the surprising finding that low-chain

Alcohols are also sufficiently stable above 170 ° for use in a steam cycle. It is therefore possible, for example, completely absorb cooling water heat with slightly raised cooling water temperature of 110 ⁰ C by evaporation of the working medium. The working fluid can still be overheated in the exhaust gas to prevailing high exhaust gas temperatures of, for example, 400 ⁰ C.

The Carnot efficiency is: η _c = lT _u / T _o where T _{o =} upper temperature level and T ₁₁ = lower temperature level. At an upper temperature level of 170 ⁰ C and a lower temperature level of 110 ⁰ C is the

Efficiency at 13.5%, with an increase in the upper temperature level to eg 400 ⁰ C, however, at 44%. This is a significant increase in efficiency.

The steam cycle may be a Kalina process, a Rankine cycle, or any other suitable steam cycle process. Preferably, the

Heat exchanger arrangement Means for exhaust heat utilization of a primary

Combustion process. In a further embodiment of the invention, the

Heat exchanger arrangement in addition means for using the waste heat of a

Cooling circuit. The heat exchanger arrangement can also use other heat sources for preheating the working medium. This allows a high process temperature with low fuel requirements.

In a preferred embodiment of the invention, the working medium is mixed with a lubricant.

The working medium may contain, in addition to the alcohol, water and / or methylpyridine. Water and methylpyridine form an azeotrope with their own Evaporation point. In this azeotrope, polar and nonpolar substances, in particular also lubricants, dissolve. The use of alcohol and methylpyridine serves among other things to protect against freezing. Alcohol vaporizes at a lower temperature than the water / methylpyridine azeotrope. It can be used to hold the cooling water heat in the low temperature range. The water / methylpyridine azeotrope has a higher evaporation point and is particularly suitable for absorbing exhaust heat or other heat sources in the upper temperature range.

Furthermore, a condenser may be provided for condensing the working medium. Alternatively, the steam cycle is designed as an open process, as may be the case, for example, in the chemical industry.

Of the alcohols used as the working medium, ethanol and more methanol than alcohol are preferred.

In one embodiment of the invention, a lubricant is added to the working medium in which the condensation temperature of the lubricant is above the steam outlet temperature. Then the lubricant is evaporated and condensed in the first in the expansion in the expander. The expander can be lubricated in this way without a separate oil circuit.

Part of the exhaust steam can be conducted into the crankcase of the expander. Then the crank mechanism is lubricated by the auskondensierende lubricant. By connecting to the condenser, the remaining lubricant can then be returned to the circuit. Embodiments of the invention are the subject of

Dependent claims. An embodiment is explained below with reference to the accompanying drawings. Brief description of the drawings

Fig.l shows schematically a steam cycle process, with methanol as

Working medium works. 2 schematically shows a Kalina process, which is treated with an ethanol: alcohol

Mix works as a working medium

Description of the embodiment

FIG. 1 illustrates a Clausius-Rankine cycle process, generally designated 10. The steam cycle 10 includes an expansion engine 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 further comprises a feedwater pump 16 and a condenser 18.

The heat exchanger 12 is flowed through 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 is generated by a pump 16. 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 expanded methanol vapor is then fed to a condenser 18 in which it is condensed to further provide methanol for the cyclic process. In this case, the amount of heat Φ _c is released, which can be used for example for heat purposes. The condensed methanol is supplied to the pump 16 again.

The described cycle is a typical Rankine cycle. The Carnot efficiency (see above) is determined by the upper temperature T ₀ in the heat exchanger 12 and the lower temperature T ₁₁ in the condenser 18.

Before heating, the methanol is liquid and has the temperature T ₁₁ . 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. When the temperature T _{0 of} the waste heat is reached, no further heat transfer is possible. The pressurized and hot gas is expanded in an expander and cooled in the condenser 18 until completely condensed again at the low temperature.

By using methanol, it is possible to achieve a low evaporation temperature at sufficient pressure.

2 shows an embodiment 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 generally designated 110. The diesel engine 110 drives one

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, which is released on the one hand via a first cooling system 114 and 116 to cooling water. On the other hand, hot exhaust gas is generated, of which a partial flow to avoid generation of emissions via an exhaust gas recirculation 118 is supplied to the engine again.

This is represented by a dashed line 120. The components described so far are known components of a motor drive system. In contrast to conventional drive systems, the cooling circuit 114 or 116 is now cooled by another circuit. In this cycle, a multi-component solution is pumped as a working fluid with a pump 128 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 to water is dependent on the heat flows cooling water exhaust gas and in diesel engines is in the range of 40:60.

The water-alcohol solution first decreases from that operated at about 110 ^° C.

Cooling circuit of the engine heat via a plate heat exchanger 132 on. In this plate heat exchanger, the first cooling circuit of the internal combustion engine 110 is cooled. The ca.H0 ° C hot cooling water 114 is cooled to about 105 ⁰ C. The working fluid heats up during this heat transfer to approximately 110 ⁰ C. This evaporates a large part of the dissolved alcohol. 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 one of the part of the exhaust heat on the

Transfer working fluid, which brings about the desired final temperature of the working fluid. The temperature of the entire working fluid with both components then reaches about 400 ⁰ C and the entire working medium is evaporated and overheated. A phase separator is not required in contrast to a pure Kalina process.

The gas under a pressure of 15 bar is fed to an expansion machine 138, for example a rotary piston machine, piston machine, screw machine or a turbine, where it is expanded to a pressure of, for example, 0.5 bar. The thereby released, usable work can be supplied to the shaft 112. Subsequently, the exhaust steam is condensed in the condenser 136 and fed back to the circuit via the pump 128. It is also possible to use solutions with other and / or further components which are adapted in type and proportion to the respective heat sources. The aim is to allow the best possible heat transfer and a high absorption of enthalpy of vaporization. The use of ethanol allows a particularly low evaporation temperature and therefore a higher efficiency.

Claims

claims

Containing steam cycle process

(b) a heat exchanger assembly for transferring heat and / or waste heat to the working fluid 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 operating power,

characterized in that

(D) the working medium is a Ci to C ₄ - alcohol or a mixture of water and / or more of these alcohols, and

(E) the higher temperature level is above 170 ⁰ C.

2. steam cycle process according to claim 1, characterized in that the steam cycle is a Kalina-like multi-component process.

3. steam cycle according to claim 1, characterized in that the

Steam cycle process is a Clausius Rankine process.

4. Steam cycle process according to one of the preceding claims, characterized in that the heat exchanger arrangement comprises means for exhaust heat utilization of a primary combustion process.

5. Steam cycle process according to one of the preceding claims, characterized in that the heat exchanger arrangement comprises means for utilizing the waste heat of a cooling circuit.

6. steam cycle according to one of the preceding claims, characterized in that a capacitor for condensing the working medium is provided.

7. steam cycle according to one of the preceding claims, characterized in that the working medium is mixed with a lubricant.

8. steam cycle according to one of the preceding claims, characterized in that the working medium in addition to the alcohol also contains water and / or methylpyridine.

9. steam cycle according to claim 7, characterized in that the

Condensation temperature of the lubricant above the

Steam outlet temperature is.

10. 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.

11. Use of a Ci to C ₄ - alcohol as a working medium in a steam cycle process according to one of the preceding claims.

12. Use according to claim 11, characterized in that the alcohol is ethanol or methanol.