Sensorless condenser regulation for power optimization for ORC systems

Abstract

The invention relates to a method for regulating a condenser in a thermal cycle apparatus, in particular in an ORC apparatus, wherein the thermal cycle apparatus comprises a feed pump for conveying liquid working medium with an increase in pressure to an evaporator, the evaporator for evaporating and optionally additionally superheating the working medium with a supply of heat, an expansion machine for generating mechanical energy by expansion of the evaporated working medium, a generator for at least partially converting the mechanical energy into electrical energy, and the condenser for condensing the expanded working medium, and wherein the method comprises the following steps: determining a rotational speed of the generator or of the expansion machine; determining, without the use of a temperature sensor, a temperature of cooling air supplied from the condenser; determining from the determined generator or expansion machine rotational speed and the determined cooling air temperature, a condensation setpoint pressure at which the net electrical power of the thermal cycle apparatus is at a maximum; and controlling or regulating the condensation pressure, with the condensation setpoint pressure as target value, in particular by adjusting a condenser fan rotational speed.

Claims

1. A method for regulating a condenser in a thermal cycle apparatus, wherein the thermal cycle apparatus comprises a feed pump for conveying liquid working medium with an increase in pressure to an evaporator, the evaporator for evaporating the working medium with a supply of heat, an expansion machine for generating mechanical energy by expansion of the evaporated working medium, a generator for at least partially converting the mechanical energy into electrical energy, and the condenser for condensing the expanded working medium, and wherein the method comprises the following steps: determining a rotational speed of the generator or of the expansion machine; determining, without the use of a temperature sensor, a temperature of cooling air supplied from the condenser; determining from the determined generator or expansion machine rotational speed and the determined cooling air temperature, a condensation setpoint pressure at which a net electrical power of the thermal cycle apparatus is at a maximum; and controlling or regulating a condensation pressure, with the condensation setpoint pressure as a target value by adjusting a condenser fan rotational speed, wherein determining the temperature of cooling air supplied from the condenser further comprises one of (i) calculating the temperature of cooling air from the determined rotational speed of the generator or of the expansion machine, a determined rotational speed of the condenser fan and a determined condensation pressure, or (ii) sampling the temperature of cooling air from a predetermined table dependent upon the determined rotational speed of the generator or of the expansion machine, a determined rotational speed of the condenser fan and a determined condensation pressure.

2. The method according to claim 1, further comprising at least one selected from the group of (i) determining the rotational speed of the generator or the expansion machine further comprises measuring the rotational speed of the generator or the expansion machine (ii) determining the rotational speed of the condenser fan by measuring the rotational speed of the condenser fan, and (iii) determining the condensation pressure by measuring the condensation pressure.

3. The method according to claim 2, wherein during starting the thermo-dynamic cycle apparatus, initially, the following steps are carried out: determining a start value for the condensation setpoint pressure; starting the thermo-dynamic cycle apparatus and controlling or regulating the condensation pressure with the start value of the condensation setpoint pressure as a target value by means of adjusting the condenser fan rotational speed; and replacing the start value for the condensation setpoint value with the condensation setpoint value determined during the operation of the thermo-dynamic cycle apparatus.

4. The method according to claim 2, wherein subsequent to a shut-down of the thermo-dynamic cycle apparatus, the following steps are carried out: determining a shut-down value for the setpoint condensation pressure; replacing the setpoint condensation pressure determined during operation of the thermo-dynamic cycle apparatus with the shut-down value for the setpoint condensation pressure; and controlling or regulating the condensation pressure with the shut-down value as a target value by means of adjusting the condenser fan rotational speed and stopping the operation of the thermo-dynamic cycle apparatus.

5. The method according to claim 1, wherein during starting the thermo-dynamic cycle apparatus, initially, the following steps are carried out: determining a start value for the condensation setpoint pressure; starting the thermo-dynamic cycle apparatus and controlling or regulating the condensation pressure with the start value of the condensation setpoint pressure as a target value by means of adjusting the condenser fan rotational speed; and replacing the start value for the condensation setpoint value with the condensation setpoint value determined during the operation of the thermo-dynamic cycle apparatus.

6. The method according to claim 5, wherein a start value for the condensation setpoint value the saturation pressure of the working medium at the current condensate temperature or the saturation pressure at the temperature of the working medium at an inlet of the feed pump, the actual pressure in standstill of the thermo-dynamic cycle apparatus, or the last condensation setpoint pressure during the last operation of the thermo-dynamic cycle apparatus can be determined.

7. The method according to claim 6, wherein replacing comprises controlling or regulating the condensation pressure from the start value of the condensation pressure to the setpoint condensation pressure determined during the operation of the thermo-dynamic cycle apparatus.

8. The method according to claim 6, wherein subsequent to a shut-down of the thermo-dynamic cycle apparatus, the following steps are carried out: determining a shut-down value for the setpoint condensation pressure; replacing the setpoint condensation pressure determined during operation of the thermo-dynamic cycle apparatus with the shut-down value for the setpoint condensation pressure; and controlling or regulating the condensation pressure with the shut-down value as a target value by means of adjusting the condenser fan rotational speed and stopping the operation of the thermo-dynamic cycle apparatus.

9. The method according to claim 5, wherein replacing comprises controlling or regulating the condensation pressure from the start value of the condensation pressure to the setpoint condensation pressure determined during the operation of the thermo-dynamic cycle apparatus.

10. The method according to claim 9, wherein subsequent to a shut-down of the thermo-dynamic cycle apparatus, the following steps are carried out: determining a shut-down value for the setpoint condensation pressure; replacing the setpoint condensation pressure determined during operation of the thermo-dynamic cycle apparatus with the shut-down value for the setpoint condensation pressure; and controlling or regulating the condensation pressure with the shut-down value as a target value by means of adjusting the condenser fan rotational speed and stopping the operation of the thermo-dynamic cycle apparatus.

11. The method according to claim 5, wherein subsequent to a shut-down of the thermo-dynamic cycle apparatus, the following steps are carried out: determining a shut-down value for the setpoint condensation pressure; replacing the setpoint condensation pressure determined during operation of the thermo-dynamic cycle apparatus with the shut-down value for the setpoint condensation pressure; and controlling or regulating the condensation pressure with the shut-down value as a target value by means of adjusting the condenser fan rotational speed and stopping the operation of the thermo-dynamic cycle apparatus.

12. The method according to claim 1, wherein subsequent to a shut-down of the thermo-dynamic cycle apparatus, the following steps are carried out: determining a shut-down value for the setpoint condensation pressure; replacing the setpoint condensation pressure determined during operation of the thermo-dynamic cycle apparatus with the shut-down value for the setpoint condensation pressure; and controlling or regulating the condensation pressure with the shut-down value as a target value by means of adjusting the condenser fan rotational speed and stopping the operation of the thermo-dynamic cycle apparatus.

13. The method according to claim 12, wherein as shut-down value the last setpoint condensation pressure during the last operation of the thermo-dynamic cycle apparatus or the saturation pressure of the working medium at current condensate temperature is specified.

14. The method according to claim 13, wherein replacing comprises a controlling and regulating the condensation pressure of the setpoint condensation pressure determined during operation of the thermo-dynamic cycle apparatus to the shut-down value for the setpoint condensation pressure.

15. The method according to claim 12, wherein replacing comprises a controlling and regulating the condensation pressure of the setpoint condensation pressure determined during operation of the thermo-dynamic cycle apparatus to the shut-down value for the setpoint condensation pressure.

16. A thermal cycle apparatus, comprising: a feed pump for conveying liquid working medium with an increase in pressure to an evaporator, the evaporator for evaporating the working medium with a supply of heat; an expansion machine for generating mechanical energy by expansion of the evaporated working medium; a generator for at least partially converting the mechanical energy into electrical energy; a condenser for condensing the expanded working medium; a control and regulation device for determining a temperature of cooling air supplied from the condenser from a determined rotational speed of the generator or the expansion machine, a determined rotational speed of the condenser fan and a determined condensation pressure; determining a condensation setpoint pressure at which a net electrical power of the thermal cycle apparatus is at a maximum from a determined or measured generator or expansion machine rotational speed and the determined cooling air temperature, and for controlling or regulating the condensation pressure with the setpoint condensation pressure as a target value; a rotational speed sensor for measuring the rotational speed of the generator or the expansion machine; a pressure sensor for measuring the condensation pressure; and a further rotational speed sensor for measuring the rotational speed of the condenser fan.

17. A thermal cycle apparatus according to claim 16, wherein the evaporator is further configured for superheating the working medium with the supply of heat.

Description

DRAWINGS

(1) FIG. 1 shows a device according to the invention.

EMBODIMENTS

(2) FIG. 1 shows an embodiment of the device according to the invention. For the description of the method according to the invention, it is also referred thereto.

(3) The thermal cycle apparatus comprises a feed pump 1 for conveying liquid working medium with an increase in pressure to an evaporator 2, the evaporator 2 for evaporating and optionally additionally superheating the working medium with a supply of heat, an expansion machine 3 for generating mechanical energy by expansion of the evaporated working medium, a generator 4 for at least partially converting the mechanical energy into electrical energy, and the condenser 5 for condensing the expanded working medium. Further, a rotational speed sensor 6 may be provided for measuring the rotational speed of the generator 4. The generator's rotational speed, however, may be determined from electrical signals from or to the generator 4. Moreover, a control device 7 is provided for determining a temperature of cooling air supplied from the condenser without using temperature sensors; determining a condensation setpoint pressure at which the net electrical power of the thermal cycle apparatus is at a maximum from a determined or measured generator or expansion machine rotational speed and the determined cooling air temperature, and for regulating the condensation pressure with the setpoint condensation pressure as target value by adjusting a condenser fan rotational speed. Further, a rotational speed sensor 8 for measuring the rotational speed of the condenser fan and a pressure sensor 9 for measuring the condensation pressure in the condenser 5 may be provided.

(4) The essential concept of the invention is to control the condensation pressure in the condenser 5 in a way that a possibly large net energy gain is achieved. For this purpose, a functional relation from important system parameters and a setpoint condensation pressure being optimal for every load point is formulated. This relation is derived from a model of the system within its environment:
p.sub.COND,opt=f(s.sub.GEN,T.sub.)(1)

(5) Thereby, s.sub.GEN is the rotational speed of the generator and T=the temperature of the supplied air (outside temperature). In an embodiment of the invention, from a model of the system, the appropriate outside temperature can be concluded for every system status.
T.sub.*=f(s.sub.GEN,s.sub.COND,p.sub.COND)(2)

(6) This calculated value T.sub.* for the outside temperature may be used in equation (1) for the optimal setpoint condensation pressure. For this, the generator rotational speed s.sub.GEN, the condenser fan rotational speed s.sub.COND, and the condensation pressure p.sub.KOND enter the calculation.

(7) For the quantification of the power transmitted by the system (load point), the generator rotational speed s.sub.GEN is used. With a higher rotational speed (upon an actual live steam status), a higher amount of the medium is supplied through the system. Correspondingly, the feed pump has to supply more of the same. Consequently, the generator rotational speed may be used as degree for the supplied power. In particular, when using volumetric expansion machines and nearly constant live steam parameters, this is an easy possibility to quantify the thermal power, as the volume flow then in a very good approximation proportionally to the rotational speed of the expansion machine. Due to the direct coupling of the generator, s.sub.GEN is equivalent to the rotational speed of the expansion machine.

(8) Considering the optimal condensation pressure at a relevant area of ambient temperature and generator rotational speed, a mathematical relation of these three values can be determined. This formal description may enter the regulation of the condensation pressure via the control of the condenser rotational speed.

(9) Applying this mathematic relation graphically, it can be recognized that a clear optimal setpoint condensation pressure can be associated to every ambient temperature and generator rotational speed, compare equation (1). With an increasing outside temperature at a constant rotational speed, a higher optimal setpoint condensation pressure results. With a constant outside temperature with an increasing generator rotational speed, and thus, expansion machine rotational speed, a higher optimal setpoint condensation pressure results.

(10) Outside temperature determination without measuring: The objective is now to specify a quantitative statement on the environmental conditions (temperature of the supplied air) from system internal values.

(11) The condensation pressure predominant in the condenser during the operation is affected by the heat dissipated in the condenser. It can be demonstrated that the heat dissipation of the condenser can be described in different ways by means of 4 variables, namely T.sub., s.sub.COND, s.sub.GEN, and p.sub.COND. Due to these relations, then by eliminating the heat dissipation, a relation between the 4 variables can be derived in the equations. By determining this mathematical relation, thus, a quantitative statement on the current, the condenser affecting environmental conditions can be presented. From this relation, then, the temperature of the supplied air T.sub. (thus, the effective temperature T.sub.*) can be determined from the other three variables. Therefore, the value, which can only be calculated from system internal variables, can enter into the described condenser regulation.

(12) According to the invention, a method for regulating a condenser in a thermal cycle apparatus, in particular in an ORC apparatus is provided, wherein the method comprises the following steps: determining, in particular measuring, a rotational speed of the generator 4 or of the expansion machine 3; determining, without the use of a temperature sensor, a temperature T.sub.* of cooling air supplied from the condenser 5; determining a condensation setpoint pressure at which the net electrical power of the thermal cycle apparatus is at a maximum; from the measured generator or expansion machine rotational speed and the determined cooling air temperature; and controlling or regulating the condensation pressure, with the condensation setpoint pressure as target value, in particular by adjusting a condenser fan rotational speed.

(13) The presented embodiments are only exemplary and the complete extent of the present invention is defined by the claims.