DE102010056516A1 - Organic rankline cycle evaporator system for biomass firings, cools flue gas prior to entry into heat exchanger, and mixing a portion of cooled flue gases - Google Patents

Abstract

The system has heat exchanger (21) heats and vaporizes the working fluid directly through the flue gas. The cooling of the flue gas is performed prior to entry into heat exchanger, and a portion of cooled flue gases (35) are mixed.

Description

definition

Firing here is a system in which by the supply of air, a medium solid, liquid, or gaseous oxidized and thereby exhaust gases, so-called flue gases, arise whose temperature is significantly higher than that of the supplied air.

The hot exhaust gases are called flue gas.

An ORC system is characterized by the presence of evaporators, condensers, turbines and pumps in which a medium other than water, the so-called working fluid, changes states from liquid to gaseous and vice versa for the purpose of converting thermal energy into electrical energy.

ORC heat exchangers refer to the heat exchanger or heat exchanger system, through which the thermal energy is transferred to the working fluid of the ORC system.

Flue gas is the gaseous product of combustion from the fuel and air supplied to the furnace. It contains a large part of the heat released by the combustion before use.

application

In order to generate electricity by means of combined heat and power from biomass is in small systems often a furnace, for. B. for the fuel wood, coupled with an ORC system. The heat released from the ORC system is usually fed into a heat network.

The output of heat from the furnace is adjusted by changing the fuel supply to the needs of the heating network after the ORC system.

The ORC system generates as much power as is possible from the supplied energy. The waste heat of the system is usually used completely for heating.

In the described arrangement is dispensed with a usually switched between firing and ORC system circulation of heat transfer oil and the ORC medium directly evaporated by hot flue gases. In order to prevent too high thermal stress from the hot flue gas in the working medium of the ORC system, the flue gas is admixed with so much already cooled flue gas that the inlet temperature into the ORC system has an optimum.

The simple design of the entire system reduces the investment and operating costs and makes it possible to use even in smaller power ranges.

State of the art

Known combinations of biomass furnaces and ORC plant are characterized in that between the ORC plant and biomass firing a thermal oil system is connected, which transmits the thermal power of the furnace in the ORC plant.

The combustion produces flue gases with temperatures of often up to 1000 ° C. With these flue gases, a heat transfer oil is heated to about 300 ° C and pumped through the heat exchanger of an ORC plant. The oil cools down and the working medium of the ORC system is preheated and evaporated.

The vapor of the working medium is expanded by a turbine to a lower pressure, condensed and pumped by means of a so-called feed pump back into the evaporator. The turbine drives a generator, which supplies electrical energy to the grid.

The heat released during the condensation is fed into a heat network via a cooling water circuit.

So that the thermal oil is not destroyed by the hot flue gas in its structure, it must be pumped through the heat exchanger permanently. This requires additional electrical energy.

Brief description of the drawings

In the accompanying schematic drawings, the basic structure and function of the new system will be apparent. It will be appreciated that the invention differs significantly from the prior art described and has numerous advantages:

1) Construction of the system without additional fan for the return and admixture of the cooled flue gases.

2) Same operation with additional blower for recirculation.

3) Additional preheater for increasing the efficiency of the entire system in the flue gas stream.

Description of the invention

Often, the flue gas coming directly from the furnace has too high a temperature in order to heat up an ORC working medium in the heat exchanger of the ORC plant. The so-called recirculation blower associated with firing serves merely to control the combustion, but without significantly influencing the flue gas temperature.

In order to prevent a combination of biomass firing ( 1 ) with ORC system 2 ) the ORC working medium in the evaporator ( 21 ) is superheated, is the hot flue gas stream produced by the biomass combustion ( 33 ) a part of already cooled flue gases ( 35 ).

1) According to the invention, this is possibly the case by the flue gas fan ( 32 ) above and the ORC evaporator ( 21 ) generated pressure loss for recycling ( 35 ) used.

For this purpose, the flue gas after the blower ( 32 ) and through a piping system ( 35 ) with the hot flue gas ( 33 ) and the resulting slightly cooler flue gas ( 34 ) the ORC evaporator ( 21 ).

Typical temperatures of the flue gas after firing ( 33 ) are 900-1000 ° C. After admixing with cooled flue gas, which has a temperature of approx. 160 ° C-180 ° C in front of the chimney ( 35 ), an inlet temperature of the flue gas ( 34 ) of for example 550 ° C in the ORC evaporator ( 21 ) reached.

For better heat utilization, as is common in such systems, between ORC evaporator ( 21 ) and fireplace ( 31 ) yet another heat exchanger ( 41 ) connected to the capacitor ( 24 ) of the ORC system ( 2 ) preheated water of the heating network still further heated and the flue gas thereby still draws heat.

3) Increasing the efficiency of the overall system also has an effect on the working medium side after the feed pump ( 32 ) of the ORC system ( 2 ) connected heat exchanger ( 26 ) through which a part of the working fluid is still through the already through the heat exchanger ( 21 ) cooled flue gas is heated.

In 2) If an alternative system is shown, which still an additional so-called recirculation fan ( 36 ) needed. Unlike the in 1) and 3) shown systems here is the cold flue gas preferably on the suction side of the flue gas blower ( 32 ).

By regulating the temperature of the flue gas stream ( 34 ) in front of the ORC heat exchanger ( 21 ) by changing the mass flow of the cold flue gas ( 35 ) by throttling by a control flap ( 64 ) in 1) or by changing the speed of the recirculation fan ( 36 ) can be an optimal inlet temperature of the flue gas ( 34 ) in the ORC heat exchanger ( 21 ) can be achieved.

In case of failure, the flue gas flow ( 34 ) through the ORC heat exchanger ( 21 ) to interrupt immediately is in 1) a flap ( 61 ). So that the flue gas can still continue to flow to the fireplace, here is the same time the flap ( 62 ) open. With an additional flap ( 63 ), the ORC heat exchanger can be additionally cooled by cold flue gas or ambient air flowing in the reverse direction to normal operation. The flaps could be functionally combined in one fitting.

In 1) is the heat exchanger ( 41 ) of the water cycle, both during operation and in case of failure always flows through. But it is also possible to bypass this in case of failure and to direct the hot flue gases directly through the chimney.

LIST OF REFERENCE NUMBERS

1) Apparatus arrangement of the direct evaporation system

2) Modified arrangement with recirculation fan

3) System with drawn and rotated by 90 ° generator or shaft system

1 - 3) details

1

biomass furnace

2

ORC system

3

Flue gas piping / flue gas stream

4

Cooling water circuit

21

Direct evaporator ORC cycle (ORC heat exchanger)

22

Feed pump ORC circuit

23

recuperator

24

capacitor

25

turbogenerator

26

Preheater (for divided working medium circle)

31

fireplace

32

Raugasventilator

33

Flue gas or flue gas duct after firing

34

Flue gas or flue gas line to the ORC

35

Cooled flue gas or flue gas line back to the ORC heat exchanger (recirculation) input

41

Cooling water heat exchanger

42

Cooling water pump

51

Flow direction Raugas operational

52

Flow direction Raugas in the event of malfunction / start / stop

61

Flue gas flap direct evaporator

62

Flue damper bypass

63

Flue gas flap Cooling air

64

Control flap for recirculating flue gases

Claims (3)

Systems from ORC plant and burns, where in at least one heat exchanger, the working fluid of the ORC system is heated directly by the flue gas from the combustion, evaporated or heated and evaporated and to cool the flue gas before entering the heat exchanger or the ORC Plant this is mixed with a part of the already cooled by this heat exchanger flue gases. Systems according to 1., in which the pressure difference is used for the return of the cooled flue gas, which builds up the flue gas fan on itself and on its suction side upstream heat exchanger, and in which at least one pipe from the pressure side of the flue gas fan to the flue gas inlet of an ORC Heat exchanger leads. Systems according to 1., wherein for returning the cooled flue gas, a fan is used, which leads a portion of the cooled flue gas after the ORC heat exchanger back to the input side for mixing with the hot flue gas from the furnace. For this purpose, these systems contain a flue gas line, in which the cooled flue gas is guided by means of a separate fan to the flue gas inlet of the ORC heat exchanger.

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