POWER PRODUCTION

FIELD OF THE INVENTION

This invention relates to apparatus and a method for use with a coal-fuelled Rankine power generation Cycle to produce increased usable electrical power from the input energy and in a manner which will increase the overall plant efficiency.

BACKGROUND TO THE INVENTION Current power production, particularly that utilizing fossil fuels, such as coal, and water as a working fluid, involves a significant amount of energy that goes to waste in conventional Rankine Cycle power stations. This is due to the required condensation of steam at the bottom of the cycle. This method of power generation is not completely efficient and can be improved upon. OBJECT OF THE INVENTION

It is the object of the present invention to create a higher efficiency cycle for power production, by utilizing at least some of the energy dissipated by the steam from the coal fired Rankine Cycle as it condenses.

SUMMARY OF THE INVENTION According to this invention there is provided a plant for generating power by combining a conventional, coal-fuelled Rankine power generation Cycle with an Organic Rankine power generation Cycle and wherein a condenser of the conventional Rankine Cycle is a heat exchanger providing the boiler for the Organic Rankine Cycle.

The invention further provides for the working fluid in the Organic Rankine Cycle to be a hydrocarbon, preferably a nonflammable refrigerant; and for the hydrocarbon working fluid to be heated to a superheated state in the heat exchanger.

Further features of the invention provide for the superheated hydrocarbon working fluid to drive multiple turbines each with its own generator; and for the turbines to be expansion turbines of either radial or axial design. Further features of the invention provide for the hydrocarbon working fluid to be condensed in a condenser using a wet cooling process, or using a dry cooling process selected from direct or indirect dry cooling, or using a wet cooling process wherein heat is transferred to water from an external natural source. The condenser will be of a plate design or shell and tube design with the cooling medium being water or air (or some other suitable fluid). In the case where the condenser would be a fluid to air condenser, the design would be of a fin and tube design which can either be cooled using fans or natural cooling using cooling towers. In the case of water-cooling, the heat exchanger is to be a high volume exchanger. Further features of the invention provide for multiple control valves to be placed between the different components of the plant to control the flow of working fluid for the two cycles; for the plant to be adapted for the primary steam Rankine Cycle turbines to be totally or partially bypassed and/or for the Organic Rankine Cycle turbines to be individually or totally bypassed.

The invention further provides for a control system to control and monitor the combined cycles; and for the cycles to be throttled by controlling the load on the generators; and for the load on the generators to be controlled through the control valves and pump speeds on return pumps for both cycles.

A further feature of the invention provides for the plant to include a hydrocarbon working fluid preheating heat exchanger to transfer energy from the heated hydrocarbon working fluid before it enters the condenser to the hydrocarbon working fluid entering the primary heat exchanger.

A further feature of the invention provides for the plant to include a water preheating heat exchanger to transfer energy from the heated hydrocarbon working fluid, before it enters the condenser, to the water before it enters the steam drum.

A water preheating heat exchanger is used to transfer energy from the steam from a high pressure cycle, in the steam turbine bypass circuit to the water before it enters the steam drum. A further aspect of the invention provides for the conventional Rankine Cycle and/or Organic Rankine Cycle equipment to be provided in modular packs, or custom designed to the conditions found within the specific application or area. According to a still further aspect of this invention there is provided a method of generating power by combining a conventional, coal-fuelled Rankine power generation Cycle with an Organic Rankine power generation Cycle.

The invention also provides for the condenser for the conventional Rankine Cycle to be used as the boiler for the Organic Rankine Cycle; and for the boiler to be a heat exchanger.

Further features of the invention provide for the flow of working fluid for the two cycles to be controlled using multiple control valves in working fluid lines; and for primary steam Rankine Cycle turbines to be totally or partially bypassed and/or for Organic Rankine Cycle turbines to be individually or totally bypassed.

Further features of the invention provide for the combined cycles to be controlled and monitored and for the cycles to be throttled by controlling the load on the generators; and for the load on the generators to be controlled through the control valves and pump speeds on return pumps for both cycles.

Further features of the invention provide for the transfer of energy from the heated hydrocarbon working fluid before it enters a condenser to the hydrocarbon working fluid entering the primary heat exchanger or to the water before it enters the steam drum.

BRIEF DESCRIPTION OF THE DRAWING One embodiment of the invention is described below with reference to the accompanying drawing in which - Figure 1 : shows the schematic view of a complete combined cycle of the power generation system. DETAILED DESCRIPTION OF THE INVENTION

Referring to Figure 1 , apparatus in the form of a power plant for the generation of electrical power to be fed into an existing or a new power grid or to be used by a local power station's grid will include the illustrated components, which are discussed together with other features below.

The invention relates to a method of generating power by combining a conventional, coal-fuelled Rankine power generation Cycle with an Organic Rankine power generation Cycle. This method will also be understood from the description of the plant that follows.

The generator system for the primary, conventional Rankine Cycle will have a boiler assembly (1 ), which is coal or partially coal fired. This will boil the water in a steam drum (3), which is then superheated in the steam super-heaters (2) of the boiler (1 ).

The superheated steam is used to drive a high pressure steam turbine (8). The steam returns from the high pressure steam turbine (8) to be reheated in the steam re-heaters (4) via the return steam line (5). The reheated steam is then fed back to the intermediate pressure turbine (9) and then on to the low pressure turbine (1 1 ). The turbine set (8), (9) and (1 1 ) will drive a main generator (12) via a common shaft.

The working fluid in the Organic Rankine Cycle is a hydrocarbon, preferably a nonflammable refrigerant. The invention provides for the condenser of the conventional Rankine Cycle to provide the boiler for the Organic Rankine Cycle. This is achieved through heat exchanger (27). The heat exchanger (27) will be a high volume exchanger of either a shell and tube or plate design.

On exiting the low pressure turbine (1 1 ) the steam is thus used to heat the hydrocarbon working fluid of the Organic Rankine Cycle in a condensing hot well of the heat exchanger (27). The steam turbine set (8), (9) and (1 1 ) can also be partially or totally bypassed by the steam turbine bypass and control circuit made up of the relevant lines and control valves (6), (7), (10) and (13). This enables bypassing of the turbines and for the steam to go directly into heat exchanger (27) from the boiler (1 ).

The heat exchanger (27) is of a counter or cross flow type. The steam will condense therein, enabling the latent heat of condensation to heat the hydrocarbon working fluid to a superheated state.

The condensed and cooled water is pumped from the hot well of the heat exchanger (27) back into the boiler feeder tank (31 ) by the water feed pump (29). From the boiler feeder tank (31 ) it is pumped back into the boiler steam drum (3) by the boiler feed pump (33).

Water feed pump (29) and control valves (28) and (30) will control the flow rate of condensed water back to the boiler feed water tank (31 ). The boiler feed pump (33) and control valve (34) will control the water flow rate to the steam drum (3). The superheated hydrocarbon working fluid will be used to drive Organic Rankine Cycle turbines (15). The turbines (15) may be expansion turbines of either radial (centrifugal) or axial flow design.

The superheated hydrocarbon working fluid may drive either single or multiple turbines (15). While only a single turbine (1 5) is shown, it may be preferable to have more than one such component. Each Organic Rankine Cycle turbine (15) will in turn drive a generator (16) to produce electrical power. The generators (16) will either be direct current or alternating current and may be driven through a step down gearbox (not shown) or directly.

The process converts the thermal and pressure energy contained in the heated hydrocarbon working fluid to rotation kinetic energy of the turbine (15) which is in turn converted to electricity by the generators (1 6).

After exiting the Organic Rankine Cycle turbines (15), the hydrocarbon working fluid will be condensed in a water-cooled condenser (23). After it is condensed, the hydrocarbon working fluid will be pumped back into the heat exchanger (27) by the hydrocarbon working fluid feed pump (25).

As already mentioned, the steam turbine bypass and control circuit will allow for the total or partial bypass of the steam turbine sets (8), (9) and (1 1 ). Alternatively, bypass of the intermediate (9) and low pressure turbine (1 1 ) may be effected by control valve (6) or only the low pressure steam turbine (1 1 ) may be bypassed using control valves (10) and (1 3).

The Organic Rankine Cycle turbines (15) similarly have a bypass circuit controlled by control valves (14) and (17), which will allow for total or partial bypass of the Organic Rankine Cycle turbines (1 5). Each turbine (15) can also be individually bypassed, while still directing superheated hydrocarbon fluid to the other turbines.

The condenser (23), which is also a heat exchanger, will either be of a shell and tube design or of plate design in the case where the cooling medium is water, as illustrated in this embodiment. The cooling water will be collected from an appropriate source. The cooling water will be pumped through the condenser (23) to provide adequate heat transfer to condense the hydrocarbon working fluid vapour back into a fluid. The cycle will utilize a cooling tower (1 8). The heat exchanger (23) will also be a high volume exchanger.

A fin and tube condenser design may be used in the case where air is to be used as an alternative cooling medium. A fluid to air condenser can either be cooled using fans driven by electrical motors or natural cooling using cooling towers.

A cool water feed pump (21 ) and control valves (19), (20) and (22) will be used to control the flow rate of cooling water through the condenser (23) and the cooling tower (1 8). The hydrocarbon working fluid feed pump (25) in conjunction with control valves (14), (17), (24) and (26) will be used to control the flow rate as well as power output of the Organic Rankine Cycle turbines (15) in relation to the energy throughput from the heat exchanger (27). Water feed pump (29) and control valves (28) and (30) will control the flow rate of condensed water back to the boiler feed water tank (31 ). The boiler feed pump (33) and control valve (34) will control the water flow rate to the steam drum (3).

Either a single (as shown) or multiple return pumps (25) may be used to pump the hydrocarbon working fluid condensate from the condenser (23) back to the heat exchanger (27) to close the cycle. These pumps (25) would be driven by electrical motors or hydrocarbon working fluid turbines, or a combination of these methods depending on the requirement at that time. Control Valve (7) will also control the steam flow rate from the steam superheaters (2) into the high pressure steam turbine (8). Control valve (6) will control the steam flow rate from the steam re-heaters (4) to the intermediate pressure steam turbine (9) as well as bypass the intermediate turbine (9) if required.

Control valves (6), (7) and (1 0) are also jointly used to control the output of the steam turbine set (8), (9) and (1 1 ) in relation to the energy input from the boiler

(1 )-

The control valves (6), (7), (10), (14) and (17) enable the primary steam Rankine Cycle turbines (8), (9) and (1 1 ) to be totally or partially bypassed and the Organic Rankine Cycle turbines (1 5) to be individually or totally bypassed.

The heat exchanger (27) operates at higher temperatures when the primary steam turbines (8), (9) and (1 1 ) are bypassed and can transfer up to the full thermal load of the boiler(1 ) to the working fluid for the Organic Rankine Cycle. The Organic Rankine Cycle turbines (1 5) will in turn operate at higher temperatures, pressures and outputs when the primary steam turbines (8), (9) and (1 1 ) are partially or totally bypassed and the generators (16) of the Organic Rankine Cycle will produce higher outputs under these conditions. The Organic Rankine Cycle turbine bypass circuit serves to provide that suitable cooling performance of the heat exchanger (27) is maintained to ensure the continued operation of the primary steam Rankine Cycle in the event of a single or multiple Organic Rankine Cycle turbine (15) unit failure. Similarly, the complete or partial steam turbine bypass circuit serves to provide that suitable heating performance of the heat exchanger (27) is maintained to ensure the continued operation of the Organic Rankine Cycle in the event of a single or multiple steam turbine unit failure. The plant will also provide for preheating of the working fluids, that is both the hydrocarbon and/or the water. A hydrocarbon preheating heat exchanger (not shown) will be used to transfer some of the energy from the hydrocarbon working fluid exiting the turbines (15) or from the Organic Rankine Cycle turbine bypass circuit [before it enters the condenser (23)] to the hydrocarbon working fluid entering the primary heat exchanger (27). The heat exchanger will be placed between the hydrocarbon working fluid return pump (25) and the heat exchanger (27).

A water preheating heat exchanger (not shown) will also be used to transfer some of the energy from the steam in the steam turbine bypass circuit to the water before it enters the steam drum (3), after it has passed through the boiler feed pump (33).

A further water preheating heat exchanger (not shown) will be used to transfer some of the energy from the hydrocarbon working fluid before it enters the Organic Rankine Cycle condenser (23) to the boiler feed water before it enters the steam drum (3), after it has passed through the boiler feed pump (33).

The combined cycles can be throttled by controlling the load on the generators (12) and (16) using the control valves and by adjusting the pump speeds on the return pumps for both cycles.

As already referred to, the invention provides for a number of control valves to be placed between the different components of the plant's cycle to control the flow of working fluid for the two cycles. A control system to control and monitor all aspects of the combined cycles will also be provided. Such a system will be within the design competence of one suitably skilled in the art. Its components and controls may either be manual, automated analog, electronic or a combination of these. The control valves which may be manually, hydraulically, pneumatically or electronically controlled are located between:

(i) the heat exchanger and turbines on both cycles; (ϋ) the boiler and steam turbines;

(iii) the turbines and the condenser on both cycles;

(iv) the condenser and the return pumps on both cycles;

(v) the return pumps for the hydrocarbon and the heat exchanger;

(vi) the return pumps for the water and the boiler feeder drum.

The control system will allow the overall operation of the plant to be monitored and the necessary activation of control valves and bypass circuits to suit current conditions or required output.

The equipment for the combined conventional Rankine Cycle and Organic Rankine Cycle will be provided in modular packs, or custom designed to the conditions found within the specific application or area. This will allow modification of an existing conventional Rankine Cycle power generation plant in accordance with the invention.

The invention provides a plant wherein most of the waste heat from the wet steam of the conventional Rankine Cycle can be transferred to the hydrocarbon working fluid of the Organic Rankine Cycle. Thus, the heat of condensation normally lost during the condensation of the steam will now be used to heat the hydrocarbon working fluid of the Organic Rankine Cycle and produce additional power from the initial input energy.

During normal operation of the conventional Rankine Cycle equipment, the amount of waste heat available will be determined by the state and volume flow of the steam exiting the low pressure turbine (1 1 ). This will (in conjunction with the efficiency of the heat exchanger and condenser and the temperature and volume flow of the available cooling medium) contribute to the generation capacity of the Organic Rankine power generation Cycle.