DE102006043491B4 - Steam cycle process with improved energy utilization - Google Patents

Abstract

An apparatus comprising a primary heat generating process and a steam cycle comprising (a) a feedwater pump (16; 128) for generating an elevated pressure in a working fluid used in the steam cycle (10; 110), (b) a heat exchanger (12; 132) for transmission the heat from the primary process to the working medium, (c) an expander (14, 138) for expanding the working medium under working power, (d) a condenser (18, 136) for condensing the working medium, (e) means (20, 138) for detecting the pressure or the temperature at the condenser, and (f) a control loop (22; 140) with which the feedwater pump with the thus detected pressure or temperature values as a reference variable can be regulated to a pressure at which the expander performance is maximum characterized in that (g) the primary process is a vehicle with a drive motor which generates waste heat, (h) the cooling medium in the condenser with the year and time of day and the geographi is subject to temperature fluctuations, and (i) the temperature fluctuations are utilized so that the upper pressure level is set to a value at which the cooling capacity of the cooling medium can be optimally utilized.

Description

Technical area

• (a) eine Speisewasserpumpe zur Erzeugung eines erhöhten Drucks in einem in dem Dampfkreisprozess verwendeten Arbeitsmedium
• (b) einen Wärmeübertrager zur Übertragung der Wärme aus dem Primärprozess auf das Arbeitsmedium,
• (c) einen Expander zum Expandieren des Arbeitsmediums unter Arbeitsleistung,
• (d) einen Kondensator zum Kondensieren des Arbeitsmediums,
• (e) Mittel zum Erfassen des Drucks oder der Temperatur am Kondensator, und
• (f) eine Regelschleife, mit der die Speisewasserpumpe mit den so erfassten Druck- oder Temperaturwerten als Führungsgröße auf einen Druck regelbar ist, bei dem die Expanderleistung maximal ist.

The invention relates to an arrangement with a heat generating primary process and a steam cycle process containing

• (a) a feed water pump for generating an increased pressure in a working medium used in the steam cycle
• (B) a heat exchanger for transferring heat from the primary process to the working medium,
• (c) an expander for expanding the working fluid under working power,
• (d) a condenser for condensing the working medium,
• (e) means for detecting the pressure or the temperature at the condenser, and
• (F) a control loop with which the feedwater pump is controlled with the pressure or temperature values thus detected as a reference variable to a pressure at which the Expanderleistung is maximum.

Such steam cycle processes are known as Clausius-Rankine cycle or as Kalina cycle. In such a cycle process, a working fluid is circulated by means of a feedwater pump. Heat is transferred to the working medium in a heat exchanger. The high pressure, hot working medium, for example water vapor or a water vapor-gas mixture, is expanded in an expander to a lower pressure level. This frees up work that can be transmitted from a wave, for example, to a generator. The relaxed, hot gas is cooled in a condenser and is then available to the cycle again. The thermodynamic efficiency η _e is determined according to η _e = 1 - T _u / T _o , where T _{u is} the lower temperature level to which the working fluid in the condenser is cooled and T _{o is} the upper temperature level to which the working fluid is heated in the heat exchanger ,

It is understood that a particularly high efficiency can be achieved when the temperature difference between the two temperatures is large. When using the waste heat of primary processes, the upper temperature is generally relatively low and can not be influenced. The lower temperature is determined by the temperature of the cooling medium in the condenser. In marine engines, the cooling medium is usually water from the water in which the ship is moving. In vehicle engines, the temperature of the cooling medium is determined by the ambient air temperature. These temperatures are usually not influenced. The efficiency is therefore generally predetermined.

State of the art

Known power plants are designed to operate at a constant power. The feedwater pump operates accordingly at constant pressure. The temperature in the heat exchanger is constant. If the temperature of the coolant changes, for example, by lowering the river water temperature in winter, this does not affect the efficiency.

Geothermal heat and waste heat from power plants generally has a comparatively low temperature. As can be seen from the above formula, this leads to a low efficiency. To increase the efficiency of waste heat utilization, therefore, a working medium containing at least two components is used in the Kalina process. One of these components has a particularly low boiling point. The working fluid is passed through a heat exchanger. Heat is supplied to the working medium in the heat exchanger. The component with the lower boiling point evaporates even at comparatively low temperatures. In a phase separator, the liquid part of the working medium is separated. The gaseous part is expanded under operating power in an expander. Subsequently, the components are condensed or cooled and brought together again. These arrangements also operate at constant power.

The DE 102 21 594 A1 discloses a controlled steam cycle for power generation with sensors for measuring parameters in the circuit. The regulation of the steam cycle is carried out by a control valve, which can lead to throttling losses. The amount of heat generated and the available cooling capacity are not limited. As a result, the efficiency can be influenced by controlling the live steam temperature.

Disclosure of the invention

• (g) der Primärprozess ein Fahrzeug mit einem Antriebsmotor ist, welcher Abwärme erzeugt,
• (h) das Kühlmedium im Kondensator mit der Jahres- und Tageszeit und der geographischen Lage Temperaturschwankungen unterliegt, und
• (i) die Temperaturschwankungen derart ausgenutzt werden, dass das obere Druckniveau auf einen Wert eingestellt wird, bei dem die Kühlleistung des Kühlmediums optimal ausgenutzt werden kann.

It is an object of the invention to provide a steam cycle process with improved energy efficiency. According to the invention the object is achieved with a steam cycle of the type mentioned fact that

• (g) the primary process is a vehicle having a drive motor that generates waste heat,
• (h) the cooling medium in the condenser is subject to temperature variations with the year and time of day and the geographical location, and
• (i) the temperature fluctuations are utilized such that the upper pressure level is set to a value at which the cooling capacity of the cooling medium can be optimally utilized.

For a given medium, the temperature at which a medium condenses is pressure dependent. At lower pressure, this temperature is lower than at higher pressure. The invention is based on the finding that the efficiency can be increased if temperature fluctuations in the cooling medium are utilized such that the upper pressure level is set to a value at which the cooling capacity of the cooling medium can be optimally utilized. In other words, the delivery rate of the feedwater pump is adjusted so that the working medium is just condensing. Then a maximum temperature difference and the associated maximum efficiency is achieved.

In one embodiment of the invention, the working fluid comprises at least two components of different boiling points, and a phase separator for separating the components is provided between the heat exchanger and the expander, so that only the gaseous portion of the working fluid is supplied to the expander. This is a Kalina cycle.

The invention utilizes the effect that the power of a secondary cycle for waste heat utilization may fluctuate, to improve the efficiency.

Embodiments of the invention are the subject of the subclaim. An embodiment is explained below with reference to the accompanying drawings.

Brief description of the drawings

1 is a schematic representation of a Clausius Rankine steam cycle process for exhaust heat recovery.

2 is a diagram that shows the course of temperature as a function of entropy in a steam cycle 1 illustrated.

3 is a schematic representation of a Kalina cycle process for waste heat recovery.

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. The cycle also includes a controllable feedwater pump 16 and a capacitor 18 ,

The heat exchanger 12 is traversed by working fluid in the form of feedwater or feedwater vapor. The working fluid is under an increased pressure, which of a pump 16 is produced. The water or water vapor is a quantity of heat Φ _H supplied from the waste heat. As a result, the water vapor is greatly overheated, that is brought to a high temperature and a higher pressure level. The inner energy increases. In an expander, for example a piston expander, turbine or the like 14 the steam 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 water vapor then becomes a condenser 18 in which it is condensed, so that the water for the cycle continues to be available. In this case, the amount of heat Φ _o is released, which can be used for example for heat purposes. The condensed water 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 _o in the condenser 18 certainly. The temperature difference is limited by the temperature of the waste heat, which is usually far below combustion temperatures. To increase the efficiency is therefore due to the pump 16 promoted mass flow adapted to the condenser temperature. The condenser temperature is determined by a sensor. The measured value is transmitted to the engine control M of the feedwater pump by means of a control loop shown schematically 16 given. This regulates the pump power in such a way that an optimal efficiency is achieved.

In 2 the effects of the control are shown on the basis of a TS diagram (temperature T, plotted on the entropy S).

Before heating, the working fluid is liquid and has the temperature T _u . This corresponds to the state designated A. When heated in the heat exchanger, the liquid is first heated and absorbs energy. At the boiling temperature T _S , the working medium begins to evaporate. This is state B. The temperature initially remains constant until the working medium has completely changed over to the gaseous state. This condition is indicated by C in the diagram. The now gaseous working fluid is now further heat energy supplied, resulting in a renewed increase in temperature. When the temperature T _{o of} the waste heat is reached, no further heat transfer is possible. The state D is reached. The pressurized and hot gas is expanded in an expander to the state E and in the condenser 18 cooled until completely condensed again at the low temperature. State D is also affected by that of the pump 16 determined pressure generated. Below a threshold value, a relaxation independent of the temperature of the condenser is always possible only up to the limit of the wet steam area that passes through the curve 24 is represented. At lower temperatures, the working fluid is fluid and does not work anymore.

When the temperature of the condenser becomes lower, in the present arrangement, the capacity of the pump 16 elevated. This has the consequence that the working fluid is heated to a higher energy point D '. However, it will be appreciated that relaxation to the lower temperature T _u '(state E') is possible and more useful work is done. This work is by the hatched area 26 represents. The efficiency is increased. By the scheme 22 can change the delivery rate of the pump 16 always optimally adapted to the condenser temperature or the associated, lower pressure.

The arrangement is particularly useful when the cycle is used in machines in which the cooling medium in the condenser is subject to temperature fluctuations. This is the case, for example, with air-cooled vehicles because the outside air temperature changes with the time of year and the time of day and the geographical location. This is also the case with ships, as the water temperature changes depending on the water and the season. The efficiency can be significantly increased in these applications.

In 3 an embodiment is shown in which a control loop is integrated into a Kalina cycle. 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. The diesel engine 110 works in a typical power range of 100 kW. It generates waste heat in the range of 250 kW. The resulting waste heat is on the one hand via a first cooling system 114 respectively. 116 delivered 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 15 bar. The working fluid in the present case consists of a carrier substance, namely water, in which a gas, namely ammonia, is dissolved. The mass ratio water: ammonia is 65:35.

The aqueous ammonia solution first takes heat from the engine's cooling circuit, which is operated at about 90 ° 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. 90 ° C hot cooling water 114 is cooled to about 83 ° C. The working fluid heats up to approximately 90 ° C during this heat transfer. As a result, a part of the dissolved ammonia gas is evaporated. The heat absorption of the working fluid is so large due to the partial evaporation of the ammonia 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 transfer, the working fluid is the heat of the exhaust gas of the exhaust gas recirculation 118 fed. The heat transfer is in the range of 17 kW. The temperature of the recirculated exhaust gas drops significantly, so that the peak temperature of the combustion in the internal combustion engine and thus the nitrogen oxide emissions are reduced by this measure. The mean temperature of the working fluid is then about 110 ° C.

In a third heat exchanger, one of the part of the exhaust gas heat is now transferred to the working fluid, which brings about the desired end temperature of the working fluid. The temperature of the working fluid then reaches 150 ° C and much of the ammonia originally dissolved in the water is evaporated.

In a phase separator 134 Then, the liquid phase of the working fluid, essentially water, from the gas phase - mainly ammonia - separated. The liquid water is easily brought at 150 ° to a lower pressure level of about 2 bar and directly a z. B. supplied air cooled cooler. The gas under a pressure of 15 bar becomes an expansion machine 138 , z. B. a rotary piston machine, piston machine, screw machine or a turbine and there relaxed to a pressure of 2 bar. The resulting work that can be freed up is in the range of up to 10 kW and can be used by the shaft 112 be supplied. In the relaxation not only the pressure level, but also the temperature of this component of the working fluid is lowered. The cold working fluid is then also supplied to the radiator. There it dissolves in the hot carrier medium, where u. U. solution heat is released. From the radiator, the cooled working fluid is transferred via the pump 128 is returned to the circuit. The cooler can also be carried out in a timely manner, since the operations "mixing" and "cooling" of the working fluid make different demands on the component design. So z. Example, a mixing section may be arranged below the radiator in order to achieve the best possible mixture of the working fluid streams and then mixed as well as possible the cooler 136 supply.

The of the cooling system 136 applied cooling power is similar despite the heat absorption from the exhaust gas compared to a conventional drive system that operates without the second circuit.

The values exemplified here for the performance of the internal combustion engine and the heat transfer can of course be adapted to the different applications. Thus, additional heat sources, such as oil cooling, charge air cooling or the like, can be integrated into the second circuit. 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. As a result, all components can be made compact. The drive power is increased. The efficiency of the entire drive is also increased. This reduces pollutant emissions with the same total power required.

The thermodynamic mean temperature of the cooled by the airstream cooler is about 110 ° C and is thus higher than in ordinary cooling circuits at about 90 ° C. This leads to a reduction of the required cooling surface. As a result, the size of the cooler can be reduced. By using a component with low boiling point (ammonia), the highest temperature is about 150 ° C lower than in known single-component systems such. B. Water is the case. These must work at about 500 ° C to achieve sufficient efficiency. Due to the lower lower temperature of up to 10 ° C, the minimum temperature of the cyclic process is considerably lower than in a one-component system described in the first embodiment. By comparison, a single-fluid system working with water, for example, has a lowest temperature of 100 ° C. at 1 bar. This lower lowest temperature achieves good thermal efficiency.

The efficiency is now further improved by, in the manner described above, a control of the pump 128 depending on the pressure in the radiator 136 he follows. A pressure sensor 138 determines the pressure at which the working fluid condenses. About a scheme 140 then becomes the pump 128 controlled. As with single-component systems, a significant increase in the average efficiency can be achieved if the coolant in the cooler is subject to temperature fluctuations.

Claims (3)

Arrangement with a heat-generating primary process and a steam cycle process comprising (a) a feedwater pump ( 16 ; 128 ) for generating an increased pressure in one in the steam cycle ( 10 ; 110 ) used working medium, (b) a heat exchanger ( 12 ; 132 ) to transfer the heat from the primary process to the working medium, (c) an expander ( 14 ; 138 ) for expanding the working fluid under working power, (d) a capacitor ( 18 ; 136 ) for condensing the working medium, (e) means ( 20 . 138 ) for detecting the pressure or the temperature at the condenser, and (f) a control loop ( 22 ; 140 ), with which the feedwater pump with the pressure or temperature values thus detected can be regulated to a pressure at which the expander performance is maximum, characterized in that (g) the primary process is a vehicle with a drive motor which generates waste heat ( h) the cooling medium in the condenser is subject to temperature fluctuations with the time of day and the time of day and (i) the temperature fluctuations are exploited such that the upper pressure level is set to a value at which the cooling capacity of the cooling medium can be optimally utilized. Steam cycle process according to claim 1, characterized in that the working fluid comprises at least two components of different boiling points, and a phase separator ( 134 ) for separating the components between the heat exchanger ( 132 ) and the expander ( 138 ) is provided, so that only the gaseous portion of the working fluid is supplied to the expander. Method for controlling a steam cycle process according to one of the preceding claims, in which (a) bringing a working fluid to an elevated pressure; (b) heat energy is transferred to the (c) the work medium is expanded under work, and (d) the working medium is recondensed; characterized in that (E) a value of the working medium representing the pressure or the temperature after condensation is detected, and (F) the increased pressure to which the working medium is brought, is regulated with the thus-detected measured value as a reference variable to a maximum work performance.

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