Live steam determination of an expansion engine

Abstract

The present invention provides a method for open-loop controlling or closed-loop controlling and/or monitoring a device with an expansion engine which is supplied live steam of a working medium that is expanded to exhaust steam in the expansion engine comprising the steps: determining at least one physical parameter of the exhaust steam; determining at least one physical parameter of the live steam based on the determined at least one physical parameter of the exhaust steam; and open-loop controlling or closed-loop controlling and/or monitoring the device based on the at least one determined physical parameter of the live steam. A thermal power plant is also provided in which the method is realized.

Claims

1. A method for open-loop controlling or closed-loop controlling and/or monitoring a device having an expansion engine, the method comprising: supplying said expansion engine with live steam of an organic working medium in a supercritical state or in a wet steam region that is expanded to exhaust steam in said expansion engine; determining at least one physical parameter of said exhaust steam; determining an isentropic degree of efficiency of said expansion engine; determining at least one physical parameter of said live steam based on the determined at least one physical parameter of said exhaust steam and the determined isentropic degree of efficiency; open-loop controlling or closed-loop controlling and/or monitoring said device based on said at least one determined physical parameter of said live steam; and operating said device within a framework of an Organic Rankine Cycle (ORC) process for generating electrical energy.

2. The method according to claim 1, further comprising the step of determining a compression ratio of said organic working medium applied to said expansion engine and a mass flow of said organic working medium, and in which said isentropic degree of efficiency of said expansion engine is determined based on the determined applied compression ratio of said organic working medium and the mass flow of said organic working medium.

3. The method according to claim 1, in which said expansion engine is a displacement engine, and further comprising the step of determining a rotational speed of said expansion engine, and in which the isentropic degree of efficiency of said expansion engine is determined based on said determined rotational speed of said expansion engine.

4. The method according to claim 3, wherein supplying said expansion engine further comprises supplying said expansion engine defined as one of a piston expansion engine, a scroll expander or a screw expander.

5. The method according to claim 1, comprising the step of modeling an operation of said expansion engine with said organic working medium based on thermodynamic equations and empirically determined parameters values, and in which said isentropic degree of efficiency of said expansion engine is determined based on a result of modeling the operation of said expansion engine.

6. The method according to claim 1, in which said at least one determined physical parameter of said exhaust steam comprises a temperature and/or a pressure of said exhaust steam.

7. The method according to claim 6, comprising the step of determining a temperature of said live steam based on the determined temperature and the determined pressure of said exhaust steam.

8. The method according to claim 1, further comprising the step of determining a pressure of said live steam which differs from said at least one determined physical parameter of said live steam being determined based on said at least one determined physical parameter of said exhaust steam, and in which said at least one physical parameter of said live steam is determined based on said determined pressure of said live steam.

9. The method according to claim 1, in which said at least one determined physical parameter of said live steam comprises a temperature and/or an enthalpy and/or an entropy and/or a volume ratio of a gaseous to a liquid phase and/or a steam content and/or a density ratio of the gaseous to the liquid phase of said live steam.

10. The method according to claim 1, wherein operating said device further comprises operating said device, wherein said device is a steam power plant or a component thereof.

11. A thermal power plant, comprising: an expansion engine operated within a framework of an Organic Rankine Cycle (ORC) process for generating electrical energy, which is supplied live steam of an organic working medium in a supercritical state or in a wet steam region that is expanded to exhaust steam in said expansion engine; and an open-loop or closed-loop controller configured to: determine at least one physical parameter of said exhaust steam; determine an isentropic degree of efficiency of said expansion engine; determine at least one physical parameter of said live steam based on said determined at least one physical parameter of said exhaust steam and the determined isentropic degree of efficiency; and open-loop control or closed-loop control and/or monitoring said thermal power plant based on said at least one determined physical parameter of said live steam.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features and embodiments as well as advantages of the present invention are by way of example illustrated below using the drawings. It is understood that the embodiments do not exhaust the scope of the present invention. It is further understood that some or all features described hereafter can also be combined in other ways.

(2) FIG. 1 illustrates measuring points for determining physical parameters used for determining physical parameters of the live steam differing therefrom according to one example of the method according to the invention.

(3) FIG. 2 illustrates the modeling of an expansion engine for determining the degree of efficiency of the same and ultimately of live steam parameters from determined exhaust steam parameters according to one example of the method according to the invention

DETAILED DESCRIPTIONS OF THE INVENTION

(4) According to the present invention, at least one physical parameter of the exhaust steam is determined in order, by means of it, to determine physical parameters of the live steam. As shown in FIG. 1, the pressure and the temperature of the exhaust steam are according to one embodiment measured at measuring points or obtained directly as information from the controller, namely, power electronics/process measuring and control technology (MSR). A working medium in the form of live steam, 1 is supplied to an expansion engine 2, such as a turbine, and mechanical energy gained by the expansion of the live steam of the working medium is by a generator converted into electrical energy 3.

(5) FIG. 1 additionally shows measurement points for measuring various parameters. On the one hand, the pressure of the live steam 1 is measured, according to the example shown, at a live steam pressure measuring point 4. The exhaust steam pressure measuring point 6 and the exhaust steam temperature measuring point 6 provide the pressure and the temperature, respectively, of the expanded exhaust steam 1′ of the working medium. Moreover, the rotational speed of the expansion engine is measured at the measuring point 7. From the measurement data thus obtained, the isentropic degree of efficiency of the expansion engine and physical parameters of the live steam required for open-loop controlling or closed-loop controlling, for example, the supply of live steam to the expansion engine, can be determined. For example, the temperature, the enthalpy or the volume ratio from the gaseous to the liquid phase and/or the steam content (quotient of the mass of the steam portion and the total mass) or the density ratio from the gaseous to the liquid phase of the live steam can be determined using the parameters measured at the measuring points 4 to 7. Determining the physical parameters of the live steam allows in particular open-loop controlling or closed-loop controlling the mass flow of the working medium to a heat exchanger (vaporizer), such that only just saturated steam is reached at the end of the expansion process.

(6) FIG. 2 illustrates an example of the invention for semi-empirical modeling of an expansion engine, by which determination of relevant physical parameters of the live steam is enabled by way of example based on determining physical parameters of the exhaust steam. For this purpose, the flow of the working medium through the expansion engine is divided into different types of changes in state of the same, which are determined by different parameters.

(7) In the example shown, the expansion engine can be modeled using seven parameters to be determined empirically.

(8) First, there is an adiabatic pressure drop 10 of the live steam (FD.fwdarw.FD1) of the working medium, which is supplied with the mass rate {dot over (m)}.sub.FD, at the inlet of expansion engine. This adiabatic pressure drop 10 is substantially determined by the inlet cross section, which is thereby used as the first empirical parameter for modeling. Isobaric cooling (FD1.fwdarw.FD2) of the working medium as the second empirical parameter occurs according to the heat transfer capacity of the live steam. The working medium then undergoes 20 in a first stage A an isentropic expansion according to the built-in volume ratio, which is to be considered as a third empirical parameter. Volumetrically operating expansion engines have a so-called built-in volume ratio. Steam is enclosed in a chamber and expanded and ejected after opening the chamber. The volume ratio is the quotient of the volume of steam when opening the chamber and the volume of steam when closing the chamber.

(9) Design-related post-expansion or return-compression of the exhaust steam (.fwdarw.AD2) is considered in a second stage B.

(10) Depending on the heat transfer capacity of the exhaust steam as the fourth empirical parameters, there it is then either a warming or cooling of the expanded steam (AD2.fwdarw.AD1). Contributing to the flow of the working medium after expansion is also a portion of the live steam after isobaric cooling (FD2), which, as a leakage mass flow having the rate {dot over (m)}.sub.leakage according to a leakage cross-section as a fifth empirical parameter, flows past the expansion stage. For this leakage mass flow, the heat loss {dot over (Q)}.sub.FD is via the isothermal casing of the expansion engine according to the heat-transfer capacity of the isobaric cooled live steam (FD2) to be considered as the sixth empirical parameter Finally, a mechanical torque loss {dot over (W)}.sub.mech of the expansion engine is considered as the seventh empirical parameter. The working medium finally exits the expansion engine as exhaust steam AD.

(11) For determining the empirical parameters, measurement values are recorded in relevant areas of operation. The isentropic degree of efficiency of the expansion engine can for different rotational speeds then be determined from the live steam pressure and the exhaust steam parameters, as determined, for example, according to FIG. 1, on the basis of thermodynamic model equations, which the person skilled in the art is familiar with. Using the determined degree of efficiency, the relevant live steam parameters such as entropy and enthalpy or temperature can then be deduced.

(12) Specifically, the following iterative method suggests itself for determining the relevant live steam parameters. In a first step, the pressure and temperature of the exhaust steam are determined, for example, measured. From this, the entropy of the exhaust steam can be determined. In a second step, live steam parameters, such as live steam temperature, steam content of the live steam and the entropy of the same, are determined by using an initial value for the isentropic degree of efficiency η(1). In a third step, the iterated isentropic degree of efficiency η(1+n) is determined using the rotational speed; the steam content of the live steam and the temperatures and pressures of both the live steam and the exhaust steam, In the fourth step, the new values for the live steam parameters, such as the live steam temperature, the steam content of the live steam and the entropy of the same are, now to be determined using the iterated isentropic degree of efficiency η(1+n). Steps 3 and 4 are to be iterated until a desired predetermined accuracy for the live steam parameters to be determined has been reached.

(13) The isentropic degree of efficiency generally depends on several parameters. It can be determined as a function of the rotational speed, the live steam parameters, the exhaust steam parameters, but also the geometry of the expansion engine, as the person skilled in the art knows. The isentropic degree of efficiency can be determined, for example, by numerical simulation, in particular, by fluidic simulation calculations. Alternatively, it can be determined empirically by a smoothing function based on measurement values or semi-empirically by parameterization of conditional equations, where parameters are generated from measurement values. These methods for determining the isentropic degree of efficiency are well known to the person skilled in the art.