CONTROL OF ORC PROCESSES BY INJECTING UNEVAPORATED FLUID

Abstract

The invention relates to a thermodynamic cycle device, in particular an ORC device, comprising a preheater for preheating a working medium; an evaporator for evaporating and superheating a first mass flow of the preheated working medium; an expansion machine for expanding the evaporated and superheated first mass flow of the working medium; a condenser for condensing the working medium exiting the expansion machine; a feed pump for pumping condensed working medium to the preheater; and a first supply apparatus for supplying a second mass flow of the preheated working medium to the partially expanded first mass flow of the working medium in the expansion machine. The invention further relates to a corresponding method.

Claims

1. Thermodynamic cycle device, in particular an ORC device, comprising: a preheater for preheating a working medium; an evaporator for possibly further preheating, evaporating and superheating a first mass flow of the preheated working medium; and an expansion machine for expanding the evaporated and superheated first mass flow of the working medium; a condenser for condensing the working medium exiting said expansion machine; a feed pump for pumping condensed working medium to said preheater; and a first supply apparatus for supplying a second mass flow of the preheated working medium to the partially expanded first mass flow of the working medium in said expansion machine.

2. Thermodynamic cycle device according to claim 1, where said first supply apparatus comprises a supply inlet of said expansion machine and a first supply line between said preheater and said supply inlet.

3. Thermodynamic cycle device according to claim 2, where said supply inlet is disposed in fluid communication with an expansion space of said expansion machine at a predetermined volume range of said expansion space, and where said expansion space expands between an inlet and an outlet of said expansion machine.

4. Thermodynamic cycle device according to claim 1, where said first supply apparatus comprises a first throttle element, in particular a first thermostatic expansion valve, for controlling the second mass flow and/or where said first supply apparatus comprises an injection device at said expansion machine, in particular at said supply inlet.

5. Thermodynamic cycle device according to claim 1, further comprising: a second supply apparatus for supplying a third mass flow of the preheated working medium to the evaporated and superheated first mass flow of the working medium prior to its expansion in said expansion machine.

6. Thermodynamic cycle device according to claim 5, where said second supply apparatus comprises a second supply line arranged between said preheater or said first supply line, on the one hand, and said inlet or a third line arranged between said evaporator and said inlet, on the other hand.

7. Thermodynamic cycle device according to claim 5, where said second supply apparatus comprises a second throttle element, in particular a second thermostatic expansion valve, for controlling the third mass flow.

8. Thermodynamic cycle device according to claim 1, where said feed pump is coupled to a drive train driven via said expansion machine; and where said cycle device further comprises: a controllable recirculation apparatus for partially recirculating working fluid from a high pressure side of said feed pump to a low pressure side of said feed pump.

9. Thermodynamic cycle device according to claim 8, where said controllable recirculation apparatus comprises a line from the high pressure side to the low pressure side of said feed pump, and where said line is provided with a third throttle element.

10. Thermodynamic cycle device according to claim 1, where a rotation of said expansion machine can be coupled with a rotation of an externally running process; where, in particular, a shaft of said expansion machine can be coupled to an external drive train of a motor, either directly or indirectly via a transmission which can have freewheeling or shifting options.

11. Method for operating a thermodynamic cycle, in particular an ORC process, where said method comprises the following steps: preheating a working medium with a preheater; possibly further preheating, evaporating and superheating a first mass flow of the preheated working medium with an evaporator; and expanding the evaporated and superheated first mass flow of the working medium in an expansion machine; condensing the working medium exiting said outlet with a condenser; pumping condensed working medium to said preheater with a feed pump; and supplying a second mass flow of the preheated working medium to the partially expanded first mass flow of the working medium in said expansion machine.

12. Method according to claim 11, comprising the further step of: controlling the second mass flow and/or injecting the second mass flow into an expansion space of said expansion machine between an inlet and an outlet of said expansion machine.

13. Method according to claim 11, further comprising: supplying a third mass flow of the preheated working medium to the evaporated and superheated first mass flow of the working medium prior to its expansion in said expansion machine.

14. Method according to claim 13, comprising the further step of: controlling the third mass flow.

15. Method according to claim 11, comprising: coupling a rotation of said expansion machine with a rotation of an externally running process; in particular by coupling a shaft of said expansion machine to an external drive train of a motor, either directly or indirectly via a transmission.

16. Thermodynamic cycle device according to claim 2, where said first supply apparatus comprises a first throttle element, in particular a first thermostatic expansion valve, for controlling the second mass flow and/or where said first supply apparatus comprises an injection device at said expansion machine, in particular at said supply inlet.

17. Thermodynamic cycle device according to claim 2, further comprising: a second supply apparatus for supplying a third mass flow of the preheated working medium to the evaporated and superheated first mass flow of the working medium prior to its expansion in said expansion machine.

18. Thermodynamic cycle device according to claim 4, further comprising: a second supply apparatus for supplying a third mass flow of the preheated working medium to the evaporated and superheated first mass flow of the working medium prior to its expansion in said expansion machine.

19. Thermodynamic cycle device according to claim 6, where said second supply apparatus comprises a second throttle element, in particular a second thermostatic expansion valve, for controlling the third mass flow.

20. Thermodynamic cycle device according to claim 2, where said feed pump is coupled to a drive train driven via said expansion machine; and where said cycle device further comprises: a controllable recirculation apparatus for partially recirculating working fluid from a high pressure side of said feed pump to a low pressure side of said feed pump.

Description

FIGURES

[0032] FIG. 1 shows a first embodiment of the thermodynamic cycle device according to the invention.

[0033] FIG. 2 shows a second embodiment of the thermodynamic cycle device according to the invention.

[0034] FIG. 3 shows a third embodiment of the thermodynamic cycle device according to the invention.

[0035] FIG. 4 qualitatively shows the relationship between the expansion ratio and expansion efficiency.

[0036] FIG. 5 is an exemplary representation of the relationship between the pressure and the enthalpy for direct injection of preheated working fluid into the expansion machine.

EMBODIMENTS

[0037] FIG. 1 shows a first embodiment of thermodynamic cycle device 100 according to the invention in the form of an ORC device (Organic Rankine Cycle). The cycle device comprises a preheater 10 for preheating a working medium; an evaporator 20 for evaporating and superheating a first mass flow of the preheated working medium; an expansion machine 30 for expanding the evaporated and superheated first mass flow of the working medium; a condenser 60 for condensing the working medium exiting the expansion machine 30; and a feed pump 70 (with motor M) for pumping condensed working medium to preheater 10. According to the invention, a first supply apparatus 40 is proved for supplying a second mass flow of the preheated working medium to the partially expanded first mass flow of the working medium in expansion machine 30.

[0038] First supply apparatus 40 comprises a supply inlet 48 of expansion machine 30 and a first supply line 47 between preheater 10 and supply inlet 48. Supply inlet 48 is disposed in fluid communication with an expansion space of expansion machine 30 at a predetermined volume range of the expansion space, where the expansion space expands between an inlet 32 and an outlet 34 of expansion machine 30.

[0039] First supply apparatus 40 further comprises a first actuatable throttle element 45, in particular a first thermostatic expansion valve, for controlling the second mass flow and/or where first supply apparatus 40 [sic] an injection device 41 at expansion machine 30, in particular at supply inlet 48.

[0040] The control can be effected on the basis of temperatures T measured and illustrated by way of example. In particular, throttle element 45 can be actuated accordingly.

[0041] The rotation of expansion machine 30 can be coupled with a rotation of an externally running process; where, in particular, a shaft 31 of expansion machine 30 can be coupled to an external drive train of a motor 90, either directly or indirectly via a transmission 91, which can have freewheeling or shifting options.

[0042] Injection of the preheated working medium into the already partially performed expansion has the effect illustrated below.

I. Providing Direct Injection of Preheated Fluid into the Ongoing Expansion According to the Process Control in FIG. 1, Thereby Satisfying Objects 1 and 2:

[0043] During the processes common to the ORC circuit of preheating VW (Q.sub.VW), evaporating VD (Q.sub.VD) and superheating H (Q.sub.H), part of the fluid ({dot over (m)}.sub.AM,DE) is removed prior to evaporation. The total energy input into the system, which can be effected directly or via an intermediate circuit, can be determined as follows:

{dot over (Q)}.sub.ges={dot over (Q)}.sub.VW+{dot over (Q)}.sub.VD+{dot over (Q)}.sub.H

{dot over (Q)}.sub.VW=(h.sub.2h.sub.1)*{dot over (m)}.sub.AM,VW=(T.sub.2T.sub.1)*.sub.p,1-2*{dot over (m)}.sub.AM,VW

{dot over (Q)}.sub.VD=(h.sub.2h.sub.2)*{dot over (m)}.sub.AM,VD=h.sub.evap*{dot over (m)}.sub.AM,VD

{dot over (Q)}.sub.H=(h.sub.4h.sub.2)*{dot over (m)}.sub.AM,H=(T.sub.4T.sub.2)*{dot over (c)}.sub.p,3-4*{dot over (m)}m.sub.AM,H

h.sub.1, h.sub.2, h.sub.3 and h.sub.4 there denote the enthalpies at the respective positions indicated in FIG. 1. For the consideration presently used of diverting working medium (AM) after preheating, no further division of the mass flow is considered and the evaporation and superheating can be combined as evaporation with superheating ({dot over (Q)}.sub.V):

[00001]${\stackrel{.}{Q}}_{V.Math..Math.\stackrel{\mathrm{.Math.}}{U}}={\stackrel{.}{Q}}_{\mathrm{VD}}+{\stackrel{.}{Q}}_{\stackrel{\mathrm{.Math.}}{U}.Math.H}=\left(h_4-h_2\right)*{\stackrel{.}{m}}_{\mathrm{AM},V.Math.\stackrel{\mathrm{.Math.}}{U}}$$\mathrm{with}$${\stackrel{.}{m}}_{\mathrm{AM},V.Math.\stackrel{\mathrm{.Math.}}{U}}={\stackrel{.}{m}}_{\mathrm{AM},\mathrm{VD}}={\stackrel{.}{m}}_{\mathrm{AM},\stackrel{\mathrm{.Math.}}{U}.Math.H}$

it is further true that: {dot over (m)}m.sub.AM,VW{dot over (m)}.sub.AM,V={dot over (m)}.sub.AM,DE

[0044] In order to again enable the degrees of freedom of temperature and the adapted expansion ratio, the diverted liquid working medium of the expansion machine is supplied via a suitable supply and injected directly already after a certain proportion of expansion (process control of FIG. 1). In order to obtain the fastest possible thermal equilibrium (heat input until a uniform temperature in the expansion chamber is given) for injection, the injection device must be configured accordingly and ensure good distribution with large fluid surfaces (e.g., fine atomization). For controllability of the parameters, a throttle element, in particular an actuatable or a passive throttle element (for example, a thermostatic expansion valve) is incorporated into the supply line.

[0045] An inlet bore must be made at a suitable location in the housing for the injection into the expander. It must be determined depending on the volume ratio of the expansion machine. The still high pressure of the chamber has a limiting effect in the direction of the beginning of expansion, as a result of which the entry of liquid fluid is impeded. In addition, superheating can also increase in the course of the expansion, so that more liquid fluid can also be evaporated at a later time of the expansion. On the other hand, sufficient time should be allowed until the chamber is opened in order to obtain a thermal equilibrium with complete evaporation. Furthermore, participation in a large expansion proportion in the overall expansion is also positive for generating power.

[0046] This can achieve various positive effects:

[0047] a. Volume Ratio Adaptation

[0048] The volume ratio of the expansion (.sup.EX) can be reduced dynamically (see also FIG. 5), the following relationship applies with the specific volumes at the time of chamber closure at the entry into the expansion machine (.sup.K, sin) and at the moment the chamber is opened at the outlet of the expansion machine (.sup.K,aus) with the fixed volume ratio of the expansion machine V.sub.i:

[00002]${}_{\mathrm{EX}}=\frac{v_{K,\mathrm{aux}}}{v_{K,\sin }}$$V_{K,\sin }=\frac{V_{K,\sin }}{m_{\mathrm{AM},K,\sin }}$$v_{K,\mathrm{aux}}=\frac{V_{K,\mathrm{aux}}}{m_{\mathrm{AM},K,\mathrm{aux}}}$$V_l=\frac{V_{K,\mathrm{aux}}}{V_{K,\sin }}=\mathrm{konstant}$

with the chamber volumes at the inlet and outlet

[00003]$V_{K,\frac{\sin }{\mathrm{aux}}}$

as well as the mass of the working medium enclosed in the chamber

[00004]$m_{\mathrm{AM},K,\frac{\sin }{\mathrm{aux}}}.$

Since, in the standard case without chamber injection, the mass of the working medium in the chamber is constant, it arises that .sup.EX=V.sub.i

[0049] The real expansion ratio (.sup.real) prevailing is determined from the live steam parameters as well as the exhaust steam parameters and is determined by the pressure and the temperature upstream and downstream of the expansion machine.

[0050] The case of .sup.real<, .sup.EX exists in the region of post compression. There, the fluid during the expansion in the expansion machine (chamber closed) is taken to a pressure level that is lower than actually existing downstream of the expansion machine. This leads to the fluid being compacted after the chamber has been opened, which has a very negative effect on the efficiency due to the increased expulsion work to be done by the expansion machine. In the region of post expansion (.sup.real>.sup.EX), the increased outlet pressure from the chamber has a positive effect. The pressure level in the expansion chamber is there at the end of the expansion still higher than that downstream of the expansion machine. As a result, the fluid expands even more when the chamber is opened, the post expansion generates additional power due to the lower expulsion work to be done by the expansion machine.

[0051] By injecting fluid during expansion, it is true that: m.sub.AM,K,aus>m.sub.AM,K, sin which, according to the relationship illustrated above, results in a reduction of .sup.EX, so that .sup.EX<V.sub.i:

[00005]${}_{\mathrm{EX}}=\frac{v_{K,\mathrm{aux}}}{V_{K,\sin }}=\frac{V_{K,\mathrm{aux}}}{m_{\mathrm{AM},K,\mathrm{aux}}}*\frac{m_{\mathrm{AM},K,\sin }}{V_{K,\sin }}=\frac{V_{K,\mathrm{aux}}}{V_{K,\sin }}*\frac{m_{\mathrm{AM},K,\sin }}{m_{\mathrm{AM},K,\mathrm{aux}}}=V_l*\frac{m_{\mathrm{AM},K,\sin }}{m_{\mathrm{AM},K,\mathrm{aux}}}<V_1$

[0052] This shift is shown in FIG. 4 with the qualitative curve of the isentropic expansion efficiency.

[0053] Furthermore, the principle of internal recuperation (as shown in FIG. 5) is thereby integrated into the process.

[0054] This leads to an improvement in the power output of the system in two ways. On the one hand, superheating of the dry fluid increasing with expansion is used to vaporize additional preheated AM for the expansion and thus to increase the mass flow of the AM participating in the expansion. The energy of the superheating of the exhaust steam would otherwise have to be dissipated via the condenser. In addition, the low temperature heat source of the preheater is usually not fully utilized and can be better utilized by the increased amount of fluid in the preheating.

[0055] The internal recuperation there avoids two problems which a normal recuperation has subsequent to the expansion. Firstly, no additional pressure loss arises due to installations after expansion which reduces the pressure level available for expansion. Furthermore, a subsequent recuperation corresponds to a preheating of the AM, for which, however, sufficient heat at a low temperature level is usually already available, for which reason it reduces the amount of heat used compared to that which is available.

[0056] b. Reducing Superheating of the Exhaust Steam

[0057] In addition to the positive effect on performance, it can also be necessary, due to the limitation of the components, e.g. of the steam-cooled generator, to reduce the evaporation temperature. An increase in the mass flow would reduce superheating of the AM but can not influence the fluid already present as live steam and therefore represents relatively sluggish control intervention. On the other hand, this can be realized very quickly with the injection.

[0058] Since the total heat balance is not affected by the bypass, readjustment via the mass flow is necessary also with this rapid control of the live steam temperature. This is done by rotational speed control of the pump (non-variable speed pumps shall be discussed in section III in the context of FIG. 3).

[0059] Temperature limitations of components that are upstream of the direct injection into the ongoing expansion can not be ensured thereby (see section II).

[0060] c. Measuring the Parameters

[0061] Two control strategies are conceivable for this: [0062] 1. Upstream of the injection point: Model-predictive determination of the quantity of AM to be injected based on a measured actual value. It is not measured to what extent the required setpoint value (=maximum value) also sets after injection. [0063] 2. Downstream of the injection point: conventional control of the quantity of AM to be injected by comparison of setpoint to actual value.

[0064] FIG. 2 shows a second embodiment of thermodynamic cycle device 200 according to the invention which has further features over with the first embodiment. The same reference numerals denote the same elements. A second supply apparatus 50 is provided for supplying a third mass flow of the preheated working medium to the evaporated and superheated first mass flow of the working medium prior to its expansion in expansion machine 30. Second supply apparatus 50 comprises a second supply line 57 which is arranged between preheater 10 or first supply line 47, on the one hand, and inlet 32 or a third line 17 arranged between evaporator 20 and inlet 32, on the other hand, where second supply apparatus 50 comprises a second actuatable throttle element 55, in particular a second thermostatic expansion valve, for controlling the third mass flow.

[0065] This measure has the effect described below.

II. Providing Direct Injection of Preheated Fluid Prior to the Expansion, as Shown in FIG. 2, to Satisfy the Remainder of Object 1 (Temperature Limitation Prior to the Expansion):

[0066] a. Reducing Superheating of the Live Steam

[0067] In addition to the direct injection into the expansion machine (process control according to FIG. 1), direct injection of preheated fluid into the live steam upstream of the expansion machine can be necessaryfor example, if also the temperature limitations prior to direct injection into the expansion machine are not otherwise ensured (process control according to FIG. 2) or if reducing the superheating is necessary, but the real expansion ratio (by process control of FIG. 1) is not to be lowered (further).

[0068] This strategy enables rapid control of the live steam temperature which would be too slow via the pump, as already described.

[0069] However, since the overall heat balance is retained by this measure, control of the total mass flow must also be effected, for example, by increasing the pump capacity.

[0070] b. Measuring the Parameters

[0071] Two control strategies are conceivable for this: [0072] 1. Upstream of the injection point: Model-predictive determination of the quantity of AM to be injected based on a measured actual value It is not measured to what extent the required setpoint value (=maximum value) also sets after injection. [0073] 2. Downstream of the injection point: conventional control of the quantity of AM to be injected by comparison of setpoint and actual value.

[0074] FIG. 3 shows a third embodiment of thermodynamic cycle device 300 according to the invention. Feed pump 70 is coupled to a drive train driven via expansion machine 30, namely to external motor 90; where the cycle device further comprises a controllable recirculation apparatus 80 for partially recirculating working fluid from a high pressure side of feed pump 70 to a low pressure side of feed pump 70. Controllable recirculation apparatus 80 comprises a line 81 from the high pressure side to the low pressure side of feed pump 70, where line 81 is provided with a third actuatable throttle element 82.

[0075] This measure has the effect described below.

III. Providing a Controllable Recirculation Around the Feed Pump in the Case of an Additional Coupling of the Feed Pump with the External Process According to FIG. 3 for Satisfying the Above-Mentioned Objects 3 and 4:

[0076] In the event that the pump is also firmly coupled with the process, a configuration of the pump with a recirculation circuit is necessary (process control according to FIG. 3).

[0077] The disadvantage of this circuitry is that additional losses are created by the recirculation around the pump. However, this is necessary in order to maintain control of the mass flow with a fixed connection.

[0078] In this case, the pump is to be dimensioned such that the least possible losses occur in a full load case and at the same time sufficient control power is available at a partial load. Control power is necessary both for increasing the mass flow through the ORC circuit (e.g. when superheating is too high) and for reducing the mass flow (e.g. quantity of heat available is smaller than the quantity of heat dissipated by AM or the actual steam pressure arising is above the evaporation pressure at the temperature level available).

[0079] Furthermore, the division into a two-component control, in which the first bypasses the evaporator (bypass branches off upstream of VD and recirculates the fluid downstream of VD+H), and the second, which comprises readjusting the mass flow (either via the pump with variable speed motor or via a recirculation control) by the evaporator, entails the advantage that sudden fluctuations and instabilities in the evaporation zone are avoided. This influence is briefly explained by the example of excessive superheating with the necessity of increasing the mass flow:

[0080] The control of the pump/recirculation increases the mass flow, at the same time the direct injection is increased. As a result, the flow through the evaporator and the superheater experiences only a small change in mass flow. As the various heat transfers in the evaporator/superheater react sensitively to level changes, this measure helps to stabilize the process. In the event that only or also the process control according to FIG. 2 is employed, their proportion of {dot over (m)}.sub.AM,DE is slowly again reduced to zero, so that overall a more rapid control intervention with rel. slow rates of change in the flow through the evaporator is obtained.

[0081] The embodiments illustrated are only by way of example and the full scope of the present invention is defined by the claims.