RU2589985C2 - Method for operation of recuperation plant - Google Patents

Abstract

FIELD: energy.

SUBSTANCE: method of controlling waste-heat recovery system for a waste heat source, comprising an organic Rankine cycle (ORC) post-connected to waste heat source, waste heat source being connected to a heating device of he ORC, as well as with an expansion machine for expanding steam in ORC, coupled to generator, wherein expansion machine is run up by generator operating in engine mode and is brought to a minimum starting engine speed specifiable in control device, wherein when minimum starting speed has been reached, a steam valve at an intake of expansion machine is opened, and further run-up of engine speed takes place and generator transitions from motor-actuated operation to normal generator operation.

EFFECT: higher efficiency of control of heat recovery unit for waste heat source.

10 cl, 1 dwg

Description

The present invention relates to a method for controlling a recovery unit (unit for using or utilizing waste heat) according to claim 1.

Under the acronym OCR (or OCR from the English. "Organic Rankine Cycle", the organic Rankine cycle) refers to the thermodynamic cycle proposed by Rankin. The aforesaid means that the working fluid passes through various thermodynamic states and at the end of the cycle is again transferred to the initial liquid state. In this case, the pressure of the working fluid is brought to a higher level by the pump. After this, the working fluid is heated to the evaporation temperature and then evaporates.

We are thus talking about a steam cycle in which instead of water the organic medium is evaporated. The resulting steam drives an expansion machine, such as a turbine, piston or screw engine, which in turn is connected to an electric generator to generate electric current. After the expansion machine, the working fluid enters the condenser and is again cooled in it with heat transfer. Since water evaporates at 100 ° С under atmospheric conditions, heat with a temperature below this level, such as, for example, the heat of industrial exhaust gases or the heat of the Earth, is often impossible to use to generate electric current. The use of organic media with lower boiling points allows the production of low-temperature steam.

OCR plants are preferable in application, for example, in the utilization of biomass in the framework of combined production of electricity and heat, especially at a relatively low power, i.e. in cases where traditional biomass-based technology is relatively expensive. Plants for generating energy from biomass often have a fermenter designed to produce biogas, which usually needs to be heated.

The recovery units of the type indicated in the restrictive part of the independent claim are known for their application in the field of combined production of electricity and heat and consist of a block thermal power plant combined with a subsequent OCR cycle. From DE 19541521 A1, there is known a device for increasing electrical efficiency when using special gases to generate electricity using internal combustion engines (ICE), the heat of the exhaust gases of which is used in a subsequent energy conversion system for the subsequent generation of electricity. In this case, however, only high-temperature heat is utilized from the cooling circuit, as well as from the engine exhaust heat exchanger.

From US 4901531, a diesel generator integrated in the Rankine cycle is further known, one cylinder of which is used for expansion according to Rankine, while the other cylinders operate as a diesel engine. A system operating according to the Rankine cycle is known from US 4,334,409, in which the working fluid is heated by means of a heat exchanger, outside of which air is passed from the output of the internal combustion engine compressor.

Block thermal power plants as installations for the combined production of electricity and heat are well known. We are talking about decentralized generator sets, mostly driven by internal combustion engines and at the same time using the heat of their exhaust gases. At the same time, the heat released during combustion and removed by cooling media is used to the maximum extent possible for heating or heat supply of the corresponding objects.

For use primarily in plants for the combined production of electricity and heat, followed by the OCR cycle, as a power plant using waste heat, machines based on engines with exhaust gas turbochargers for charging have proven themselves well. In this regard, there is a need for engines with an extremely high electric efficiency, achievable only when using turbo-supercharging and re-cooling of a combustible mixture heated by compression. In general, cooling the combustible mixture is necessary insofar as otherwise filling the cylinders would be relatively poor. Thanks to the cooling of the combustible mixture entering the cylinders, its density increases and at the same time the filling factor of the cylinders increases. As a result, the output of engine power and its mechanical efficiency increase.

In order to ensure sufficient cooling of the combustible mixture, the inlet temperature prescribed by engine manufacturers should be only about 40-50 ° C. Since this temperature level is relatively low, the heat taken from the combustible mixture in currently known installations for the combined production of electricity and heat is removed to the environment, for example, using a dry cooler.

From DE 102005048795 B3 there is further known a two-stage heating of the working fluid in the OCR cycle in a heating device, namely, the working fluid in the OCR cycle is heated in two heat exchangers connected in series to the feed pump, the first of which, installed after the feed pump, serves as the first stage for supplying low-temperature heat, and the next heat exchanger serves as a second stage for supplying high-temperature heat. A cooling system of the combustible mixture entering the internal combustion engine is connected to the first heat exchanger installed after the feed pump, and the heat taken from the combustible mixture entering the internal combustion engine in the internal combustion engine serves to heat the working fluid in the OCR cycle and as a low-temperature heat is supplied to the working fluid in the first heat exchanger. The second heating circuit uses heat taken from the liquid to cool the internal combustion engine and from its exhaust gases, and is connected to a second heat exchanger installed after the feed pump, while the heat taken from the cooling liquid in its circulation circuit and from the exhaust gas of the internal combustion engine serves to overheat and evaporation of the working fluid in the OCR cycle and as high-temperature heat is supplied to the working fluid in a second heat exchanger installed after the feed pump.

Based on the foregoing, the present invention was based on the task of optimizing a recovery unit with a CCR cycle sequentially provided after the source of waste heat in relation to its design and performance.

According to the invention, this problem is solved using the object of the invention with the distinctive features presented in claim 1 of the claims. In the dependent claims are various preferred embodiments of the invention.

The recuperation unit proposed in the invention is characterized in that the expansion machine for expanding the steam in the OCR cycle is started by the generator operating in the motor mode and accelerates to the minimum starting speed set in the control device. The minimum starting speed preferably corresponds to about two-thirds of the minimum operating speed. The decisive advantage associated with the operation of the generator in the motor mode is the low load on the bearings in the starting phase, since refrigerant is not yet supplied to the expansion machine, otherwise, in a still cold expansion machine, undesired condensation of small amounts of refrigerant could occur under certain conditions. However, in this case, it is already being cooled, also by a partial flow of refrigerant, although in the liquid phase.

According to the invention, upon reaching the minimum starting frequency of rotation, the steam valve opens at the inlet of the expansion machine to expand the steam in the OCR cycle and upon further opening of this steam valve, a further increase in the frequency of rotation occurs, as a result of which the generator switches from motor mode to normal generator mode. This aspect is preferable insofar as the expansion machine immediately from the moment of start-up, respectively, is initially connected to the generator as an electric motor and does not require synchronization with the network. When the steam valve is fully open and when the minimum operating speed has been reached, then a speed optimization process is initiated in the control device taking into account the actual operating situation.

In yet another preferred embodiment of the invention, the control device determines, for the expansion machine for expanding the steam in the OCR cycle, the optimal speed for the actual operating point. In this case, at the first stage, starting from the minimum rotation frequency, it slowly increases in an analysis of the generator power until the excess of the peak level is detected at an increasing rotation frequency and at the same time decreasing generator power. Then, in the third stage, the rotation frequency is reduced, and in subsequent stages, the processes performed in the second and third stages are repeated until the rotation frequency is stabilized at the point of maximum generator power.

Further preferred is the option in which in the control device for an expansion machine for expanding steam in the OCR cycle, it is possible to set the rotational speed optimal for the actual operating point by a multi-parameter characteristic.

Thus, in particular, in a preferred embodiment of the invention, the pressure at the input and / or output of the expansion machine is mapped in the multi-parameter characteristic of the optimal speed and, in order to determine the actual operating state, the actual inlet pressure is measured, analyzed and corrected in the control device for the multi-parameter characteristic / or the output of the expansion machine to adjust the speed in this way. Alternatively, or in addition to this, in the multi-parameter characteristic the optimal speed can be associated with the temperature at the inlet and / or outlet of the expansion machine and, to determine the actual operating state, the actual inlet temperature and / can be measured, analyzed and corrected in the control device for the multi-parameter characteristic or the output of the expansion machine to adjust the speed in this way.

A variant is also preferred in which the generator combined with an expansion machine for expanding the steam in the OCR cycle has a frequency converter associated with it for working with a variable, respectively, variable speed.

In another preferred embodiment, an adjustable bypass with at least one throttle valve in the OCR circuit is provided that bypasses the expansion machine. Such a bypass is first in the starting phase, i.e. at a still relatively low temperature of the working fluid, it is open, and therefore the working fluid is bypassed by the expansion machine in order to avoid unwanted ingress of the residual liquid phase present in the working fluid into the expansion machine. Immediately after the OCR-circuit reaches its predetermined operating state, which is determined, for example, by the corresponding, set temperature level or other parameters, the bypass closes and the steam valve installed in front of the expansion machine opens.

The solution proposed in the invention makes it possible to optimize the design and performance of the recovery unit with the OCR cycle sequentially provided after the waste heat source. As an example of sources of waste heat can be called block thermal power plants, industrial plants or boiler plants.

According to the invention, the starting phase of the expansion machine is also optimized. At the same time, maximum operational reliability and protection against refrigerant condensation are achieved when the expansion machine is accelerated by a generator operating in the motor mode in the absence of refrigerant. Since, on the cooling side, the partial refrigerant stream used for this purpose is passed through the generator unit, when operating in the motor mode, this partial refrigerant stream absorbs heat loss at this point.

The thermal state of the expansion machine, as well as other boundary conditions, is also controlled. These as starting conditions include, for example, the smallest refrigerant pressure in the OCR circuit, the conditions for switching on the system of magnetic bearings of the turbine impeller, i.e. systems of its magnetic bearings, as well as control of all functionally necessary units.

According to the invention, thus, the start-up process of the recovery unit takes place in a fully automatic mode under the control of the electronics. The aforesaid applies equally to the automated normal mode of operation with a variable speed, consistent with the specific operating situation, as well as to the stop mode.

The invention is described in more detail below by the example of one of its embodiments with reference to the only drawing attached to the description, which shows a schematic diagram of a recovery unit with a CCR cycle sequentially provided after the source of waste heat.

The components that are functionally important for the OCR cycle are the OCR circuit 1 (a circuit operating according to the organic Rankine cycle), a feed pump 2, an evaporator 3, an expansion machine 4 for expanding steam, connected to a generator 5, a condenser 6 for re-cooling by means of a heat sink 7, as well as heat exchangers 8, 9 for heating the working fluid in the OCR circuit 1.

Both heat exchangers 8, 9 are connected in series to the feed pump 2. The first heat exchanger 8, installed after the feed pump 2, serves as the first stage for supplying low-temperature heat to the working fluid, and the next heat exchanger 9 serves as the second stage for supplying high-temperature heat from the source 10 of the exhaust heat to the working fluid.

The second heating circuit 11 is connected by its supply line to the evaporator 3 of the OCR circuit, since the temperature level is first high enough for direct heating. After this, the second heating circuit 11 with its return line enters the second heat exchanger 9 and gives in it the remaining heat to the working body of the OCR.

To cool the expansion machine 4, a partial stream of liquid refrigerant 12 is discharged, first passed through the generator 5. After that, the cooling medium passes through the housing of the expansion machine 4 and provides sufficient heat removal in this place.

Upon reaching the minimum starting speed of rotation, the steam valve 13 at the inlet of expansion machine 4 opens to expand the steam in the OCR cycle, and upon further opening of this steam valve 13, a further increase in the frequency of rotation occurs, as a result of which the generator 5 switches from normal operation to normal operation generator mode.

Bypassing the expansion machine 4, an adjustable bypass 14 with at least one throttle valve 15 is provided. First, such bypass 14 is in the starting phase, i.e. at a still relatively low temperature of the working fluid, it is open. In this way, the working fluid is bypassed the expansion machine 4. Immediately after the OCR circuit 1 reaches its predetermined operating state, the throttle valve 15 in the bypass 14 closes and the steam valve 13 installed in front of the expansion machine 4 opens.

Claims (10)

1. The control method of the recovery unit for the source (10) of waste heat, consisting of an organic Rankine cycle (OCR), the successively provided after this source (10) of waste heat, which is connected to the heating device of the OCR cycle, as well as with an expansion machine (4 ) to expand the steam in the OCR cycle, which is connected to the generator (5) and which is started by the generator (5) operating in the motor mode and accelerates to the minimum starting speed set in the control device, upon reaching which opens the steam valve (13) at the inlet of the expansion machine (4) to expand the steam in the OCR cycle, and when this steam valve (13) is further opened, the speed increases further, as a result of which the generator (5) switches from the motor mode to work in normal generator mode. 2. The method according to claim 1, characterized in that the minimum starting speed corresponds to approximately two-thirds of the minimum operating speed. 3. The method according to claim 2, characterized in that when the steam valve (13) is fully open and when the minimum operating speed has been reached, a speed optimization process is initiated in the control device. 4. The method according to claim 1, characterized in that the control device determines, for the expansion machine (4) for expanding the steam in the OCR cycle, the optimal speed for the actual operating point, for which, in the first stage, starting from the minimum speed, the slow its adjustable increase in the analysis of the generator power, in the second stage with increasing frequency and at the same time decreasing generator power, an excess of the peak level is detected and in the third stage the rotation frequency is reduced, and in subsequent stages, the processes performed in the second and third stages are repeated until the speed is stabilized at the point of maximum generator power. 5. The method according to one of claims 1 to 3, characterized in that in the control device for the expansion machine (4) for expanding the steam in the OCR cycle, it is possible to set the optimal speed for the actual operating point according to a multi-parameter characteristic. 6. The method according to claim 5, characterized in that the pressure at the input and / or output of the expansion machine (4) is set in the multi-parameter characteristic of the optimal speed and, to determine the actual operating state, it is measured, analyzed and adjusted in the control device according to the multi-parameter characteristic the actual pressure at the inlet and / or outlet of the expansion machine (4) for adjusting the speed in this way. 7. The method according to claim 5, characterized in that the temperature at the inlet and / or outlet of the expansion machine (4) is set in the multi-parameter characteristic of the optimal speed and for measuring the actual operating state is measured, analyzed and adjusted in the control device according to the multi-parameter characteristic the actual temperature at the inlet and / or outlet of the expansion machine (4) for adjusting the speed in this way. 8. The method according to claim 1, characterized in that the generator (5) combined with the expansion machine (4) for expanding the steam in the OCR cycle has a frequency converter associated with it for working with a variable, respectively, variable speed. 9. The method according to claim 1, characterized in that an adjustable bypass (14) that bypasses the expansion machine (4) is provided with at least one throttle valve (15) in the OCR circuit (1). 10. The method according to claim 9, characterized in that the adjustable bypass (14), bypassing the expansion machine (4), is first opened and closed in the starting phase when the temperature in the OCR circuit (1) reaches the set level.

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