Patent Description:
There is a great need for the development of power systems that can meet increasing consumption needs. While much work is directed to systems that do not utilize combustion of fossil fuels, cost factors and availability of fossil fuels, especially coals and natural gas (as well as waste hydrocarbons, such as residual oil products), drive a continued need for systems configured to combust such fuels, particularly with high efficiency and complete carbon capture. To meet these needs, there is a continued desire for the development of control systems that can provide for precise control of power systems.

<CIT> discloses a prior art power system comprising an integrated control system.

In one or more embodiments, the present disclosure can provide systems and methods useful for controlling one or more aspects of a power production system. The control systems particularly can provide control over one or more of pressure, temperature, flow rate, and stream composition of one or more flow streams in a power production system. The control systems can provide for optimum efficiency of the power production system. The control systems further can provide control over aspects of the power production system, such as start-up of the system, shutdown of the system, change of input stream(s) in the system, change of output stream(s) in the system, handling of operating emergencies related to the system, and any like considerations related to operation of a power production system.

In one or more embodiments, the present disclosure can relate to a control system suitable for use in a power production plant. For example, the power production plant can be a plant burning a fuel (such as a hydrocarbon, particularly a hydrocarbon gas) in substantially pure oxygen in a combustor at a pressure of about <NUM> MPa or greater with an additional circulating CO<NUM> stream to produce a combined stream of combustion products and circulating CO<NUM>. In some embodiments, the power production can be further characterized by one or more of the following points, which can be combined in any number or order.

The combined stream can be passed through a power producing turbine with a discharge pressure of at least <NUM> bar.

The turbine exhaust can be cooled in an economizer heat exchange to preheat the circulating CO<NUM> stream.

The turbine exhaust can be further cooled to near ambient temperature, and condensed water can be removed.

The CO<NUM> gas stream can be compressed to be at or near the turbine inlet pressure using a gas compressor followed by a dense CO<NUM> pump to form the circulating CO<NUM> stream.

Net CO<NUM> produced in the combustor can be removed at any pressure between the turbine inlet and outlet pressures.

Heat from an external source can be introduced to preheat part of the circulating CO<NUM> stream to a temperature in the range <NUM> to <NUM> in order to reduce the temperature difference between the turbine exhaust and the circulating CO<NUM> stream leaving the economizer heat exchanger to about <NUM> or less.

The fuel gas flow rate can be controlled to provide the required power output from the turbine.

The turbine outlet temperature can be controlled by the speed of the CO<NUM> pump.

The CO<NUM> compressor discharge pressure can be controlled by recycling compressed CO<NUM> flow to the compressor inlet.

The flow rate of net CO<NUM> produced from fuel gas combustion and removed from the system can be used to control the CO<NUM> compressor inlet pressure.

The difference between the temperature of the turbine exhaust entering the economizer heat exchanger and the temperature of the circulating CO<NUM> stream leaving the economizer heat exchanger can be controlled to be at or below <NUM> by controlling the flow rate of a portion of the circulating CO<NUM> stream which is heated by an added heat source.

The flow rate of net liquid water and fuel derived impurities removed from the system can be controlled by the level in the liquid water separator.

The oxygen flow rate can be controlled to maintain a ratio of oxygen to fuel gas flow rate which can result in a defined excess oxygen in the turbine inlet flow to ensure complete fuel gas combustion and oxidation of components in the fuel gas.

The oxygen stream at CO<NUM> compressor inlet pressure can be mixed with a quantity of CO<NUM> from the CO<NUM> compressor inlet to produce an oxidant stream with an oxygen composition of about <NUM>% to about <NUM>% (molar), which can lower the adiabatic flame temperature in the combustor.

The oxidant flow required to produce the required oxygen to fuel gas ratio can be controlled by the speed of the oxidant pump.

The discharge pressure of the oxidant compressor can be controlled by recycling compressed oxidant flow to the compressor inlet.

The inlet pressure of the oxidant compressor can be controlled by the flow rate of diluent CO<NUM> mixed with the oxygen which forms the oxidant stream.

The ratio of oxygen to CO<NUM> in the oxidant stream can be controlled by the flow of oxygen.

The oxygen can be delivered to the power production system at a pressure at least as high as the turbine inlet pressure, and an oxidant stream with an oxygen composition in the range of about <NUM>% to about <NUM>% (molar) can be desired.

The oxygen to fuel gas ratio can be controlled by the oxygen flow.

The oxygen to CO<NUM> ratio in the oxidant flow can be controlled by the flow of diluent CO<NUM> taken from CO<NUM> compressor discharge.

In any of the embodiments discussed herein, the control of one parameter by a second parameter can particularly indicate that the second parameter is measured (e.g., with a sensor) or otherwise monitored or that the second parameter is calculated by a computer based upon additionally provided information, lookup tables, or presumed values, and a controller initiates a control sequence based upon the measured or calculated second parameter so that the first parameter is appropriated adjusted (e.g., by opening or closing of a valve, increasing or decreasing power to a pump, etc.). In other words, the second parameter is used as a trigger for a controller to implement an adjustment to the first parameter.

In one or more embodiments, the present disclosure can provide power production systems that include an integrated control system, which can be configured for automated control of at least one component of the power production system. In particular, the control system can include at least one controller unit configured to receive an input related to a measured parameter of the power production system and configured to provide an output to the at least one component of the power production system subject to the automated control. The power production system and integrated control system can be further defined in relation to one or more of the following statements, which can be combined in any number and order.

The power production system can be configured for heat input via combustion of a fuel.

The power production system can be configured for heat input via a non-combustion heat source.

The power production system can be configured for recycling a stream of CO<NUM>.

The power production system can be configured for producing an amount of CO<NUM> that can be optionally withdrawn from the system, such as being input to a pipeline or being utilized for a further purpose, such as enhanced oil recovery.

The power production system can be configured for utilizing a working fluid that is repeatedly compressed, heated, and expanded.

The integrated control system can include a power controller configured to receive an input related to power produced by one or more power producing components of the power production system.

The power controller can be configured to meet one or both of the following requirements: provide an output to a heater component of the power production system to increase or decrease heat production by the heater component; provide an output to a fuel valve to allow more fuel or less fuel into the power production system.

The integrated control system can include a fuel/oxidant ratio controller configured to receive one or both of an input related to fuel flow rate and an input related to oxidant flow rate.

The fuel/oxidant ratio controller can be configured to meet one or both of the following requirements: provide an output to a fuel valve to allow more fuel or less fuel into the power production system; provide an output to an oxidant valve to allow more oxidant or less oxidant into the power production system.

The integrated control system can include a pump controller configured to receive an input related to temperature of an exhaust stream of a turbine in the power production system and to provide an output to a pump upstream from the turbine to increase or decrease flow rate of a stream exiting the pump.

The integrated control system can include a pump suction pressure controller configured to receive an input related to suction pressure on a fluid upstream from a pump in the power production system and to provide an output to a spillback valve that is positioned upstream from the pump.

The pump suction pressure controller is configured to meet one or both of the following requirements: cause more of the fluid or less of the fluid to spill back to a point that is further upstream from the spillback valve; cause more of the fluid or less of the fluid to be removed from the power production system upstream from the pump.

The integrated control system can include a pressure regulation controller configured to receive an input related to pressure of an exhaust stream of a turbine in the power production system and to provide an output to a fluid outlet valve and allow fluid out of the exhaust stream and optionally to provide an output to a fluid inlet valve and allow fluid into the exhaust stream.

The integrated control system can include a water separator controller configured to receive an input related to the amount of water in a separator of the power production system and to provide and output to a water removal valve to allow or disallow removal of water from the separator and maintain the amount of the water in the separator within a defined value.

The integrated control system can include an oxidant pump controller configured to receive an input related to one or both of a mass flow of a fuel and a mass flow of an oxidant in the power production system and calculate a mass flow ratio of the fuel and the oxidant.

The oxidant pump controller can be configured to provide an output to the oxidant pump to change the power of the pump so as to affect the mass flow ratio of the fuel and the oxidant in the power production system.

The integrated control system can include an oxidant pressure controller configured to receive an input related to the pressure of an oxidant stream downstream from an oxidant compressor and to provide an output to an oxidant bypass valve to cause more oxidant or less oxidant to bypass the compressor.

The integrated control system can include an oxidant pressure controller configured to receive an input related to the pressure of an oxidant stream upstream from an oxidant compressor and to provide an output to a recycle fluid valve to cause more recycle fluid or less recycle fluid from the power production system to be added to the oxidant stream upstream from the oxidant compressor. In particular, the recycle fluid can be a substantially pure CO<NUM> stream.

The integrated control system can include a dilution controller configured to receive an input related to one or both of the mass flow of an oxidant and the mass flow of an oxidant diluent stream and to calculate a mass flow ratio of the oxidant and the oxidant diluent.

The dilution controller can be configured to provide an output to an oxidant entry valve to allow more oxidant or less oxidant to enter the power production system so that the mass flow ratio of the oxidant to the oxidant diluent is within a defined range.

The integrated control system can include a compressor suction pressure controller configured to receive an input related to suction pressure of a fluid upstream from a compressor in the power production system and to provide an output to a spillback valve that is positioned downstream from the compressor and that causes more of the fluid or less fluid to spill back to a point that is upstream from the compressor.

The integrated control system can include a pump speed controller configured to receive an input related to suction pressure upstream from the pump and to provide an output to the pump to increase or decrease pump speed.

The integrated control system can include a side flow heat controller configured to receive an input related to a calculated mass flow requirement for a side flow of a high pressure recycle stream in the power production system and to provide an output to a side flow valve to increase or decrease the amount of the high pressure recycle stream in the side flow.

The power production system can comprise: a turbine; a compressor downstream from the turbine and in fluid connection with the turbine; a pump downstream from the compressor and in fluid connection with the compressor; and a heater positioned downstream from the pump and in fluid connection with the pump and positioned upstream from the turbine and in fluid connection with the turbine. Optionally, the power production system can include a recuperator heat exchanger.

In one or more embodiments, the present disclosure can provide methods for automated control of a power production system. In particular, the method can comprise operating a power production system comprising a plurality of components that include: a turbine; a compressor downstream from the turbine and in fluid connection with the turbine; a pump downstream from the compressor and in fluid connection with the compressor; and a heater positioned downstream from the pump and in fluid connection with the pump and positioned upstream from the turbine and in fluid connection with the turbine. Further, operating the power production system can include using one or more controllers integrated with the power production system to receive an input related to a measured parameter of the power production system and provide an output that automatically controls at least one of the plurality of components of the power production system. In further embodiments, the methods can include one or more of the following steps, which can be combined in any number and order.

The output can be based upon a pre-programmed, computerized control algorithm.

The operating can include input of heat via combustion of a fuel.

The operating can include input of heat via a non-combustion heat source.

The operating can include recycling a stream of CO<NUM>.

The operating can include producing an amount of CO<NUM> that can be optionally withdrawn from the system, such as being input to a pipeline or being utilized for a further purpose, such as enhanced oil recovery.

The operating can include utilizing a working fluid that is repeatedly compressed, heated, and expanded.

The operating can include using a controller to receive an input related to power produced by the power production system and direct one or both of the following actions: provide an output to the heater to increase or decrease heat production by the heater; provide an output to a fuel valve of the power production system to allow more fuel or less fuel into the power production system.

The operating can include using a controller to receive one or both of an input related to fuel flow rate and an input related to oxidant flow rate and to direct one or both of the following actions: provide an output to a fuel valve of the power production system to allow more fuel or less fuel into the power production system; provide an output to an oxidant valve of the power production system to allow more oxidant or less oxidant into the power production system.

The method operating can include using a controller to receive an input related to temperature of an exhaust stream of the turbine and provide an output to the pump upstream from the turbine to increase or decrease flow rate of a stream exiting the pump.

The operating can include using a controller to receive an input related to suction pressure on a fluid upstream from the pump and provide an output to a spillback valve that is positioned upstream from the pump. In particular, one or both of the following requirements can be met: the controller causes more of the fluid or less of the fluid to spill back to a point that is further upstream from the spillback valve; the controller causes more of the fluid or less of the fluid to be removed from the power production system upstream from the pump.

The operating can include using a controller to receive an input related to pressure of an exhaust stream of the turbine and provide an output to a fluid outlet valve and allow fluid out of the exhaust stream and optionally provide an output to a fluid inlet valve and allow fluid into the exhaust stream.

The operating can include using a controller to receive an input related to the amount of water in a separator included in the power production system and provide and output to a water removal valve to allow or disallow removal of water from the separator and maintain the amount of the water in the separator within a defined value.

The operating can include using a controller to receive an input related to one or both of a mass flow of a fuel and a mass flow of an oxidant introduced to the power production system and calculate a mass flow ratio of the fuel and the oxidant. In particular, the controller can provide an output to an oxidant pump to change the power of the pump so as to affect the mass flow ratio of the fuel and the oxidant in the power production system.

The operating can include using a controller to receive an input related to the pressure of an oxidant stream downstream from an oxidant compressor and provide an output to an oxidant bypass valve to cause more oxidant or less oxidant to bypass the compressor.

The operating can include using a controller to receive an input related to the pressure of an oxidant stream upstream from an oxidant compressor and to provide an output to a recycle fluid valve to cause more recycle fluid or less recycle fluid to be added to the oxidant stream upstream from the oxidant compressor. In particular, the recycle fluid can be a substantially pure CO<NUM> stream.

The operating can include using a controller to receive an input related to one or both of the mass flow of an oxidant and the mass flow of an oxidant diluent stream and to calculate a mass flow ratio of the oxidant and the oxidant diluent. In particular, the controller can be configured to provide an output to an oxidant entry valve to allow more oxidant or less oxidant to enter the power production system so that the mass flow ratio of the oxidant to the oxidant diluent is within a defined range.

The operating can include using a controller to receive an input related to suction pressure of a fluid upstream from the compressor and provide an output to a spillback valve that is positioned downstream from the compressor and that causes more of the fluid or less fluid to spill back to a point that is upstream from the compressor.

The operating can include using a controller to receive an input related to suction pressure upstream from the pump and to provide an output to the pump to increase or decrease pump speed.

The operating can include using a controller to receive an input related to a calculated mass flow requirement for a side flow of a high pressure recycle stream and provide an output to a side flow valve to increase or decrease the amount of the high pressure recycle stream in the side flow.

Having thus described the disclosure in the foregoing general terms, reference will now be made to accompanying drawings, which are not necessarily drawn to scale, and wherein:.

The present invention now will be described more fully hereinafter.

As used in this specification and the claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

In one or more embodiments, the present disclosure provides systems and methods for control of power production. The control systems and methods can be utilized in relation to a wide variety of power production systems. For example, the control systems can be applied to one or more systems wherein a fuel is combusted to produce heat to a stream that may or may not be pressurized above ambient pressure. The control systems likewise can be applied to one or more systems wherein a working fluid is circulated for being repeatedly heated and cooled and/or for being repeatedly pressurized and expanded. Such working fluid can comprise one or more of H<NUM>O, CO<NUM>, and N<NUM>, for example.

Examples of power production systems and methods wherein a control system as described herein can be implemented are disclosed in <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, and <CIT>.

As a non-limiting example, a power production system with which a control system as presently described may be utilized can be configured for combusting a fuel with O<NUM> in the presence of a CO<NUM> circulating fluid in a combustor, preferably wherein the CO<NUM> is introduced at a pressure of at least about <NUM> MPa and a temperature of at least about <NUM>, to provide a combustion product stream comprising CO<NUM>, preferably wherein the combustion product stream has a temperature of at least about <NUM>. Such power production system further can be characterized by one or more of the following:
The combustion product stream can be expanded across a turbine with a discharge pressure of about <NUM> MPa or greater to generate power and provide a turbine discharge steam comprising CO<NUM>.

The turbine discharge stream can be passed through a heat exchanger unit to provide a cooled discharge stream.

The cooled turbine discharge stream can be processed to remove one or more secondary components other than CO<NUM> to provide a purified discharge stream.

The purified discharge stream can be compressed to provide a supercritical CO<NUM> circulating fluid stream.

The supercritical CO<NUM> circulating fluid stream can be cooled to provide a high density CO<NUM> circulating fluid (preferably wherein the density is at least about <NUM>/m<NUM>).

The high density CO<NUM> circulating fluid can be pumped to a pressure suitable for input to the combustor.

The pressurized CO<NUM> circulating fluid can be heated by passing through the heat exchanger unit using heat recuperated from the turbine discharge stream.

All or a portion of the pressurized CO<NUM> circulating fluid can be further heated with heat that is not withdrawn from the turbine discharge stream (preferably wherein the further heating is provided one or more of prior to, during, or after passing through the heat exchanger).

The heated pressurized CO<NUM> circulating fluid can be recycled into the combustor (preferably wherein the temperature of the heated, pressurized CO<NUM> circulating fluid entering the combustor is less than the temperature of the turbine discharge stream by no more than about <NUM>).

The presently disclosed control systems can be particularly useful in relation to power production methods such as exemplified above because of the need for providing precise control over multiple parameters in relation to multiple streams, such parameters needing precise control to provide desired performance and safety. For example, in one or more embodiments, the present control systems can be useful in relation to any one or more of the following functions.

The present control systems can be useful to allow for differential speed control of a power producing turbine and a compressor that is utilized to compress a stream that is ultimately expanded through the turbine. This is an advantage over conventional gas turbines wherein the compressor and the turbine are mounted on the same shaft. This conventional configuration makes it impossible to operate the compressor at a variable speed. Constant rotational speed and inlet conditions yield a substantially constant mass throughput into the compressor and therefore the turbine. This can be affected through the use of inlet guide vanes, which restrict the airflow entering the compressor and thereby lower the mass throughput. According to the present disclosure, the use of a pump between the compressor and the turbine provides for significant levels of control of the power production system. This allows for decoupling of the mass throughput of the compressor-pump train and the shaft speed of the turbine-compressor-generator train.

The present control systems can be useful to control the inlet and/or outlet pressure of a turbine expanding a heated gas stream. The heated gas stream can be predominately CO<NUM> (by mass).

The present control systems can be useful to control an outlet temperature of a turbine.

The present control systems can be useful to control operation of a power production system with a CO<NUM> compression means to raise the CO<NUM> pressure from a turbine exhaust volume to the pressure of a turbine inlet volume so that these pressures are maintained.

The present control systems can be useful to control removal of the net CO<NUM> formed from carbon in a combustor fuel gas at any point in the CO<NUM> compression means from turbine exhaust pressure to turbine inlet pressure.

The present control systems can be useful to control operation of a power production system wherein a hot turbine exhaust is cooled in an economizer heat exchanger while heating a recycle high pressure CO<NUM> stream to ensure the heat recovery from the cooling turbine exhaust provides the optimum flow of heated high pressure CO<NUM> recycle to a combustor at the highest possible temperature.

The present control systems can be useful to optimize heat input to a recycle CO<NUM> stream (for example, at a temperature of about <NUM> or less) from an external heat source to control the temperature difference in an economizer heat exchanger below a temperature of <NUM> to maximize the quantity of recycle CO<NUM> which can he heated against a cooling turbine exhaust stream and minimize the hot end temperature difference of the economizer heat exchanger.

The present control systems can be useful to control the fuel flow to a combustor to ensure that the combustion products when mixed with a high pressure heated recycle CO<NUM> stream form the inlet gas stream to a turbine at the required temperature and pressure.

The present control systems can be useful to control the oxygen flow to a combustor to give a required excess O<NUM> concentration in a turbine outlet stream to ensure complete combustion of a fuel.

The present control systems can be useful to control operation of a power production system so that a turbine exhaust stream leaving an economizer heat exchanger can be further cooled by ambient cooling means to maximize the condensation of water formed in the combustion process and reject the net water production from fuel gas combustion together with other fuel or combustion derived impurities.

In one or more embodiments, a power production suitable for implementation of a control system as described herein can be configured for heating via methods other than through combustion of a fossil fuel. As one non-limiting example, solar power can be used to supplement or replace the heat input derived from the combustion of a fossil fuel in a combustor. Other heating means likewise can be used. In some embodiments, any form of heat input into a CO<NUM> recycle stream at a temperature of <NUM> or less can be used. For example, condensing steam, gas turbine exhaust, adiabatically compressed gas streams, and/or other hot fluid streams which can be above <NUM> may be utilized.

In some embodiments, it can be particularly useful to control a turbine outlet temperature at a maximum value that is fixed by the maximum allowable temperature of an economizer heat exchanger being utilized. Such control can be based on the turbine inlet and outlet pressures and the heat exchanger operating hot end temperature difference.

Control systems of the present disclosure can be defined by one or more functions wherein a parameter (e.g., a measured parameter and/or a calculated parameter) can be linked to one or more executable actions. The executable actions can include one or more actions that regulate a flow of a fluid in the system, such as through opening and closing of one or more valves. As non-limiting examples, measured parameters in a control system according to the present disclosure can include a fluid flow rate, a pressure, a temperature, a liquid level, a fluid volume, a fluid composition, and the like. A measured parameter can be measured using any suitable device, such as thermocouples, pressure sensors, transducers, optical detectors, flow meters, analytical equipment (e.g., UV-VIS spectrometers, IR spectrometers, mass spectrometers, gas chromatographs, high performance liquid chromatographs, and the like), gauges, and similar devices. Calculated parameters in a control system according to the present disclosure can include, for example, power consumption of a compressor (e.g., a CO<NUM> compressor), power consumption of a pump (e.g., a CO<NUM> pump), power consumption of a cryogenic oxygen plant, fuel heat input, a pressure drop (e.g., a pressure drop in a heat exchanger) for one or more fluid streams, a temperature differential (e.g., a temperature difference at a heat exchanger hot end and/or heat exchanger cold end), a turbine power output, a generator power output, and system efficiency. A calculated parameter may be calculated, for example, by a computerized supervisory control system based on measured parameters.

Embodiments of the present disclosure are illustrated in <FIG>, which illustrates a control system that may be used particularly for a closed power cycle. The control system is particularly useful in systems and methods where direct control over the amount of heat entering the system, for instance in solar applications, is not required. In this configuration, a working fluid is circulated through a heater <NUM>, a turbine <NUM> connected to a generator <NUM>, a first heater/cooler <NUM>, a compressor <NUM>, a second heater/cooler <NUM>, and a pump <NUM>. Optionally, a recuperator heat exchanger <NUM> can be included so that heat in working fluid stream 101b exiting turbine <NUM> can be recuperated into the working fluid stream <NUM> to exit as working fluid stream <NUM> that is further heated by the heater <NUM>.

Heat entering the power production system in heater <NUM> is added to the working fluid, which is preferably as a high pressure (e.g., about <NUM> bar or greater, about <NUM> bar or greater, about <NUM> bar or greater, about <NUM> bar or greater, about <NUM> bar or greater, about <NUM> bar or greater, about <NUM> bar or greater, or about <NUM> bar or greater) to provide a high pressure, heated working fluid stream 101a. This stream passes to the turbine <NUM> and is expanded to a lower pressure to exit as working fluid stream 101b. Parameter check point <NUM> is configured downstream from the turbine <NUM> and upstream from the first heater/cooler <NUM> (and optionally upstream from the recuperator heat exchanger <NUM> if present) and includes a temperature sensor, thermocouple, or the like. Controller <NUM> (which can be characterized as a pump controller) directs and/or gathers one or more temperature readings (which readings can be continuous or periodic) at parameter check point <NUM>. So as to maintain a substantially constant temperature at parameter check point <NUM>, controller <NUM> directs power adjustments as necessary for pump <NUM>. For example, controller <NUM> can control the speed of pump <NUM> in response to the temperature reading at parameter check point <NUM>. In this manner, controller <NUM> can be configured to maintain a desired temperature in working fluid stream 101b independent of the amount of heat that is being introduced into the system in heater <NUM>, and likewise independent of the inlet temperature of turbine <NUM>. This is beneficial in that pump <NUM> can be specifically controlled to deliver the correct mass flow of working fluid at the correct pressure as dictated by the inlet temperature to the turbine <NUM> as indicated by the amount of heat introduced in heater <NUM>.

Such dynamic control can affect one or more further parameters in the power production system illustrated in <FIG>. For example, changes in the flow rate through pump <NUM> causes changes in the suction pressure immediately upstream from the pump in working fluid stream 101f. In order to maintain desired controllability of pump <NUM>, the suction conditions of the pump must remain as constant as possible within the predetermined range. Second heater/cooler <NUM> can be useful to maintain the suction temperature at pump <NUM> at a desired value. So as to maintain a substantially constant suction pressure for pump <NUM>, controller <NUM> (which can be characterized as a pump suction pressure controller) can be configured to monitor a pressure sensor, transducer, or the like positioned at parameter check point <NUM>, and controller <NUM> can utilize pressure readings taken therefrom to control a spillback valve <NUM>, which can be configured to allow more or less fluid from working fluid stream 101e to spill back to parameter check point <NUM>, which can be at any position in working fluid stream 101c. Controller <NUM> thus essentially can be configured to control the amount of recirculation flow around compressor <NUM> via the spillback valve <NUM>. As such, pressure at parameter check point <NUM> can be increased by reducing fluid flow through spillback valve <NUM> and can be decreased by increasing fluid flow through the spillback valve. As fluid is spilled back into working fluid stream 101c, it can also be desirable to maintain a substantially constant pressure in working fluid streams 101b and 101c. Accordingly, parameter check point <NUM> can likewise include a pressure sensor, transducer, or the like. The temperature sensor and the pressure sensor can be configured in the same parameter check point, or different parameter check points can be utilized in working fluid stream 101b for the respective sensors.

Because parameter check point <NUM> is in fluid communication with parameter check point <NUM> and parameter check point <NUM>, the respective pressures at points <NUM>, <NUM>, and <NUM> may differ substantially only due to inherent pressure losses through equipment and piping. Controller <NUM> can be configured to monitor a pressure sensor, transducer, or the like positioned at parameter check point <NUM>, and controller <NUM> can be configured to control valve <NUM> so as to allow fluid from working fluid stream 101d into, or out of, the system in order to maintain a substantially constant pressure at parameter check point <NUM>. As such, parameter check point <NUM> can include a pressure sensor, transducer, or the like, which can be monitored by controller <NUM> if desired. Alternatively, because parameter check points <NUM> and <NUM> are in fluid communication, the measured pressure at parameter check point <NUM> can be considered to be substantially identical to the pressure at parameter check point <NUM>. Valve <NUM> can be configured to remove and/or add fluid to the working fluid stream in order to maintain the desired pressure. In some embodiments, there can be two valves instead of the single valve <NUM> - a first valve (i.e., a fluid outlet valve) configured to allow fluid out to a lower pressure sink, and a second valve (i.e., a fluid inlet valve) configured to allow fluid in from a higher pressure source.

In some embodiments, the illustrated system can be controlled such that valve <NUM> is either absent or is not utilized, and controller <NUM> can instead operate to substantially prevent surging by the compressor <NUM>. In such embodiments, controller <NUM> can still operate to manage temperature at parameter check point <NUM>, and the control look can be a completely closed loop, which configuration can be particularly useful for indirectly heated power production cycles. For example, in one or more embodiments, heater <NUM> can be configured for provision of solar heating at or above a defined heat level, and the power production system can thus be substantially self-regulating to produce as much power as possible with dynamic response to changes in the solar input. Such configuration could likewise be maintained if additional heat for a further source was continuously or intermittently added in heater <NUM>.

In the illustrated system of <FIG>, compressor <NUM> receives its inlet working fluid stream from the turbine <NUM>, and its outlet working fluid stream is delivered ultimately to the pump <NUM>. The compressor <NUM> can be shaft-mounted on the turbine <NUM>, and the working conditions of the compressor may be substantially unchanged based on the control of the turbine exhaust conditions.

Although controller <NUM>, controller <NUM>, and controller <NUM> are illustrated and discussed as being separate controllers, it is understood that the respective controllers can be configured as part of a larger unit. For example, a single control unit may include a plurality of subunits that can be individually connected with their designated parameter check points and their controlled devices (e.g., the pump <NUM>, the spillback valve <NUM>, and the valve <NUM>). Moreover, the control units can be configured substantially as subroutines in an overall controller (e.g., a computer or similar electronic device) with a plurality of inputs and a plurality of outputs that are designated for the respective parameter check points and controlled devices.

In embodiments wherein recuperative heat exchanger <NUM> is included, control of temperature at parameter check point <NUM> can be particularly important. By maintaining the temperature at parameter check point <NUM> at or substantially near a steady state value, the temperature profiles in the recuperative heat exchanger <NUM> can remain substantially constant as well. At a minimum, such control scheme is beneficial because of the reduction or elimination of thermal cycling of the piping, heat exchangers, and other high temperature equipment utilized in the system, which in turn can significantly increase component lifetimes.

Embodiments of the present disclosure are illustrated in <FIG>, which shows a power production system that is substantially identical to the power production system illustrated in <FIG>. In the system of <FIG>, a further controller <NUM> (which can be characterized as a power controller) is included and can be configured for monitoring a variety of values and directing a number of control commands.

In one or more embodiments, controller <NUM> can be configured to measure and/or receive measurements in relation to the power output of generator <NUM>. In some embodiments, controller <NUM> can be configured to direct heat input via heater <NUM> to generate the required power. Thusly, if power output at generator <NUM> is above or below the desired output, heat input via heater <NUM> can be decreased or increased to deliver the desired power output. Similarly, monitoring of power output with controller <NUM> can enable dynamic changes to the heat input so that a substantially constant power output can be provided. As a non-limiting example, when solar heating is utilized for heater <NUM>, the power output at generator <NUM> can be utilized as a trigger so that, for example, more mirrors may be aimed at a collection tower to increase heat output when power output drops below a defined level and/or when the power output is insufficient to meet a predefined heating algorithm, such as wherein power output may be automatically increased at a time of day when usage is expected to be increased. As a further non-limiting example, a plurality of heat sources can be utilized wherein a first heat source can be utilized primarily, and a second heat source can be automatically brought online when power output at the generator <NUM> is insufficient. For example, solar heating may be combined with combustion heating with one being the primary heat source and the other being the secondary heat source to supplement the primary heat source.

As more or less heat is added to the system, the turbine inlet temperature will change and, after expansion through the turbine, the temperature at parameter check point <NUM> will change. As such, one or more of the control functions described above in relation to <FIG> likewise can be implemented in the system as illustrated in <FIG>.

Embodiments of the present disclosure are further illustrated in <FIG>, which illustrates a control system that may be used particularly for a semi-closed power cycle. The control system is particularly useful in systems and methods where the cycle is a direct fired oxy-fuel cycle burning a carbonaceous fuel with oxygen. As illustrated at least two components that can be combined to provide an exothermic reaction are introduced to the system through valve <NUM> and valve <NUM>. The components are shown as being introduced directly to turbine <NUM>; however, in one or more embodiments, the components may be introduced to a reactor, such as a combustor. In some embodiments, turbine <NUM> is a multi-stage component including a reaction or combustion chamber upstream from a turbine. In <FIG>, the portion of element <NUM> below the dashed line can be a combustion chamber, and the portion of element <NUM> above the dashed line can be a turbine. As a non-limiting example, valve <NUM> can be configured for metering a fuel, such as natural gas or other fossil fuel, and valve <NUM> can be configured for metering an oxidant, such as air or substantially pure oxygen (e.g., at least <NUM>%, at least <NUM>%, at least <NUM>%, or at least <NUM>% pure oxygen).

In the system exemplified in <FIG>, controller <NUM> can be configured to monitor the power output of generator <NUM>. Based upon the measured power output, controller <NUM> controls fuel valve <NUM> to allow more fuel or less fuel into the power production system. As more fuel or less fuel is added to the power production system, controller <NUM> (which can be characterized as a fuel/oxidant ratio controller) compares the fuel flow rate at parameter check point <NUM> to the oxidant flow rate at parameter check point <NUM>, and controller <NUM> commands the oxidant valve <NUM> to allow more oxidant or less oxidant therethrough in order to maintain the prescribed ratio of fuel to oxygen.

Reaction (e.g., combustion) products pass through the turbine <NUM> (or the turbine section of a combination reactor/turbine) and exit as a turbine exhaust stream. As an example, when natural gas and oxygen are metered through valve <NUM> and valve <NUM>, the main products in the turbine exhaust stream will be H<NUM>O and CO<NUM>. The turbine exhaust stream can pass through a recuperator heat exchanger <NUM> (although such component is optional) and then pass through the first heater/cooler <NUM>. The turbine exhaust stream is then treated in water separator <NUM> where water can be taken off through valve <NUM>. A substantially pure CO<NUM> stream exits the top of the separator <NUM> and is passed through compressor <NUM> (with a fraction being drawn off through valve <NUM>. A compressed recycle CO<NUM> stream exiting compressor <NUM> is passed through the second heater/cooler <NUM> and then pump <NUM> to provide a high pressure recycle CO<NUM> stream, which can be passed back to the turbine <NUM> (optionally passing through the recuperator heat exchanger <NUM> to be heated with heat withdrawn from the turbine exhaust stream). A substantially pure CO<NUM> stream can comprise at least <NUM>% by weight, at least <NUM>% by weight, at least <NUM>% by weight, at least <NUM>% by weight, or at least <NUM>% by weight CO<NUM>.

As illustrated in <FIG>, the control system used with the exemplary power production system includes controller <NUM>, controller <NUM>, and controller <NUM>, which can function substantially identically as described above in relation to the systems of <FIG> and <FIG>. In addition, controller <NUM> (which can be characterized as a water separator controller) is utilized to monitor water level in separator <NUM>, which can include one or more sensors suitable for providing a water level output that can be read by controller <NUM>. Based on the water level signal received, controller <NUM> can direct valve <NUM> to open at the correct intervals and durations to maintain the water level in the separator <NUM> at a desired level. Although measurement is referenced in relation to a water level, it is understood that volume, mass, or other parameters may be utilized to provide the signal to controller <NUM>.

Additional embodiments of the present disclosure are illustrated in <FIG>, which illustrates a control system that may be used particularly for a semi-closed power cycle utilizing an artificial air source. The control system is particularly useful in systems and methods where the cycle is a direct fired oxy-fuel cycle burning a carbonaceous fuel with oxygen. Controller <NUM> again monitors the power output of generator <NUM> and meters fuel input through valve <NUM> accordingly.

As illustrated in <FIG>, fuel and oxidant enter the combustion section of dual combustor/turbine <NUM>, and a turbine exhaust stream exits the turbine section. The turbine exhaust stream can pass through a recuperator heat exchanger <NUM> (although such component is optional) and then pass through the first heater/cooler <NUM>. The turbine exhaust stream is then treated in water separator <NUM> where water can be taken off through valve <NUM>. A substantially pure CO<NUM> stream exits the top of the separator <NUM> and is passed through compressor <NUM> (with a fraction being drawn off through valve <NUM>). A compressed recycle CO<NUM> stream exiting compressor <NUM> is passed through the second heater/cooler <NUM> and then pump <NUM> to provide a high pressure recycle CO<NUM> stream, which can be passed back to the dual combustor/turbine <NUM> (optionally passing through the recuperator heat exchanger <NUM> to be heated with heat withdrawn from the turbine exhaust stream).

In this configuration, oxidant enters through valve <NUM> and passes through union <NUM>, where CO<NUM> can be combined with the oxidant. The oxidant stream (optionally diluted with the CO<NUM> stream) passes through heater/cooler <NUM>, is pressurized in compressor <NUM>, passes through heater/cooler <NUM>, and is finally passed through in pump <NUM>. Controller <NUM> (which can be characterized as an oxidant pump controller) measures the ratio between the mass flow of the fuel (read at parameter check point <NUM>) and the mass flow of the oxidant (read at parameter check point <NUM>). Based upon the calculated ratio, controller <NUM> can direct variable speed pump <NUM> to change the power of the pump and allow the delivery of oxidant in the correct mass flow to maintain the desired oxidant to fuel ratio at the required pressure. In this manner, the amount of oxidant supplied to the power production system is consistently at the correct flow rate and correct pressure for passage into the dual combustor/turbine <NUM>. If, for example, the pressure at parameter check point <NUM> were to rise due to back pressure from the combustor/turbine <NUM>, controller <NUM> can be configured to command pump <NUM> to operate at a different speed suitable to provide the correct pressure and oxidant mass flow. Based upon a pressure reading taken at parameter check point <NUM>, controller <NUM> (which can be characterized as an oxidant pressure controller) can direct spillback valve <NUM> to decrease or increase the pressure at parameter check point <NUM> by allowing more or less fluid to spill back (or be recycled) to a point upstream from the compressor <NUM> (particularly between union <NUM> and heater/cooler <NUM>. Pressure likewise can be monitored at parameter check point <NUM> (which pressure corresponds to the suction of compressor <NUM>). Based upon this pressure, controller <NUM> (which can be characterized as an oxidant pressure controller) can direct valve <NUM> to divert none or a portion of the fluid upstream of compressor <NUM> to union <NUM> so as to maintain a substantially constant pressure at parameter check point <NUM>. The substantially pure CO<NUM> stream diverted through valve <NUM> can be utilized to dilute the oxidant, and controller <NUM> likewise can be configured to increase or decrease flow through valve <NUM> to provide the desired dilution. Mass flow of the CO<NUM> stream provided through valve <NUM> can be measured at parameter check point <NUM>, and the mass flow of the oxidant provided through valve <NUM> can be measured at parameter check point <NUM>. Controller <NUM> (which can be characterized as a dilution controller) can be configured to calculate the ratio of the flows at check points <NUM> and <NUM>, and can be configured to direct valve <NUM> to allow more oxidant or less oxidant to enter the system so as ensure that the correct ratio is maintained.

In one or more embodiments, a control system according to the present disclosure can be configured to specifically provide for mass control across a wide range of pressures. Low pressure mass control (e.g., at ambient pressure to about <NUM> bar, to about <NUM> bar, or to about <NUM> bar) can be achieved similarly to the description of controller <NUM> above. In particular, controller <NUM> can be configured to open or close valve <NUM> to relieve excess mass from the power production system. For example, in a system utilizing a recycle CO<NUM> stream as a working fluid and combusting a fossil fuel, excess CO<NUM> can be formed. To maintain the correct mass balance in the system, all or a portion of the formed CO<NUM> can be drawn off through valve <NUM>. The amount of fluid drawn though valve <NUM> for purposes of mass control can be calculated based upon the known stoichiometry of the combustion reaction, and controller <NUM> can be configured to control mass flow through valve <NUM> accordingly. If desired, one or more sensors can be utilized to measure and/or calculate fluid mass downstream from the combustor and/or to measure and/or calculate fluid mass ratio between a stream between the combustor and the valve <NUM> in relation to a stream that is downstream from the compressor <NUM> and/or the pump <NUM>.

In the embodiment illustrated in <FIG>, controller <NUM> and controller <NUM> as described above are absent, and further controllers are provided in order to release the excess mass from the power production system at substantially the same pressure as the outlet pressure of the compressor <NUM> (which is substantially identical to the suction of pump <NUM>). As described above, the speed of pump <NUM> is controlled by the exhaust temperature of the turbine <NUM> via controller <NUM>. In the embodiment exemplified in <FIG>, however, suction pressure of compressor <NUM> is controlled. In particular, parameter check point <NUM> can include a pressure sensor, and controller <NUM> (which can be characterized as a compressor suction controller) can be configured to open and close valve <NUM> based upon the pressure at the suction of the compressor <NUM> as measured at parameter check point <NUM>. If the pressure at parameter check point <NUM> begins dropping, controller <NUM> can be configured to open valve <NUM> and allow fluid to spill back to a point upstream from parameter check point <NUM> (spillback going to parameter check point <NUM> in the illustrated embodiment) and raise the pressure at parameter check point <NUM>. If the pressure at parameter check point <NUM> begins increasing, controller <NUM> can be configured to close valve <NUM> so as to reduce the amount of fluid spilling back and lower the pressure at parameter check point <NUM>.

In addition to controlling the speed of pump <NUM>, the suction pressure of the pump can also be controlled. In particular, the pressure read at parameter check point <NUM> can be utilized by controller <NUM> (which can be characterized as a pump speed controller), which can be configured to open and close valve <NUM>. Accordingly, the suction pressure of pump <NUM> is controlled by removing excess fluid from the power production system at valve <NUM>, which in turn provides for maintaining the desired system pressure.

In the embodiment illustrated in <FIG>, the power control system is configured similarly to the construction illustrated in <FIG> but without the use of valve <NUM>. In this illustrated embodiment, the compressor <NUM> operates on suction pressure control as described in relation to <FIG>, and pump <NUM> also operates on suction pressure control. In particular, the pressure read at parameter check point <NUM> can be utilized by controller <NUM>, which can be configured to adjust the speed of pump <NUM> to maintain controlled suction conditions and output at correct pressure dictated by the further parameters of the combustion cycle. In addition, temperature taken from parameter check point <NUM> can again be used by controller <NUM>; however, the controller <NUM> can be configured to direct flow through valve <NUM> to control the temperature of the exhaust from turbine <NUM>. By allowing more fluid out of the power production system through valve <NUM> (or keeping more fluid in the power production system), the inlet pressure (and therefore mass flow) through turbine <NUM> can be controlled, and the outlet temperature of turbine <NUM> can be likewise controlled.

In one or more embodiments, a power system shown in <FIG> can comprise a turbine <NUM> coupled to an electric generator <NUM>. A fuel stream is metered through valve <NUM>, and oxygen is metered through valve <NUM>, and the fuel is combusted with the oxygen in combustor <NUM>. The fuel and oxygen are mixed with heated, high pressure recycle CO<NUM> stream <NUM> leaving the economizer heat exchanger <NUM>. Combustion gases pass to the turbine 10b. The turbine discharge stream is cooled in the economizer heat exchanger <NUM> against the high pressure recycle CO<NUM> stream <NUM> and is further cooled to near ambient temperature in the first heater/cooler <NUM>. In some embodiments, the first heater/cooler <NUM> can be an indirect heat exchanger using for example cooling water or it can be a direct contact heat exchanger which both cools the turbine exhaust stream and condenses water. The near ambient temperature stream enters water separator <NUM> which discharges the condensed liquid water stream through valve <NUM>. The stream can include fuel or combustion derived impurities which are an oxidized state, such as SO<NUM> and NO<NUM>. In the case of a direct contact cooler the unit acts as a combined gas cooler gas/water contactor and liquid phase separator. The recycled CO<NUM> stream <NUM> enters CO<NUM> recycle compressor <NUM> where its pressure is raised (e.g., from about <NUM>-<NUM> bar to about <NUM> bar). The compressor <NUM> is provided with a recycle CO<NUM> line <NUM> with a valve <NUM> to reduce the pressure and return a portion of the compressor flow to the suction at point <NUM>. The net CO<NUM> product, which contains all the carbon derived from the fuel gas stream following oxidation in the turbine combustor, is vented from the compressor as stream through valve <NUM>. The net CO<NUM> product can be delivered at pressure from the compressor suction to the pump discharge. The recycled CO<NUM> stream exiting the compressor <NUM> is cooled to near ambient temperature in second heater/cooler <NUM>. The density increases to typically about <NUM>/liter to about <NUM>/liter. The dense supercritical CO<NUM> is pumped to typically <NUM> bar in a multistage pump <NUM>. The recycled CO<NUM> stream <NUM> exiting pump <NUM> enters the economizer heat exchanger <NUM>.

A portion 119a of the recycled CO<NUM> stream exiting pump <NUM> is heated in heat exchanger <NUM> against a heating stream <NUM>, which can be from any source, such as heat withdrawn from an air separation unit. This stream 119a is heated typically to a temperature of about <NUM> to about <NUM>. The heated stream is then passed into the heat exchanger <NUM> at an intermediate point and remixed with the high pressure recycle CO<NUM> stream <NUM>. The system is controlled by control valves which regulate the fluid flows. The system is provided with sensors which measure flow rates, pressures, temperatures and gas compositions. These measurements can be fed, for example, to a digital control system which regulates the power plant using control algorithms together with stored supervisory control programs. The output from the control system regulates the degree of opening of the control valves plus the speed of the pump <NUM> and other system functions. The objective is to achieve defined high efficiency operation at any required power output, optimum start-up conditions, controlled ramp rates either up or down, shutdown and responds to system malfunctions. Although such digital control system and control algorithms are mentioned in relation to the system of <FIG>, it is understood that such disclosure applies equally to any further embodiments described herein, including embodiments described in relation to and of <FIG> an FIG.

The functional control of the system can be defined by the links between the variables measured by sensors and the response of the particular control valve. One or more embodiments of control systems that can be utilized in relation to any embodiments disclosed herein include the following.

The fuel flow rate through valve <NUM> can be controlled by the electricity demand imposed on the electric generator <NUM>.

The speed of pump <NUM> can be used to control its discharge flow rate. In particular, the flow rate set point can be varied to maintain a defined turbine outlet temperature.

The outlet pressure of the CO<NUM> compressor <NUM> can be maintained at a constant defined value by varying the set point of the compressor recycle flow control valve <NUM>.

Venting of CO<NUM> produced in the power production cycle can be controlled by the flow control valve <NUM>. The set point of this flow controller can be varied to maintain a constant inlet pressure to the CO<NUM> compressor and the turbine discharge. In some embodiments wherein venting through valve <NUM> takes place at the discharge of compressor <NUM>, the control system can be configured to vary the flow through valve <NUM> and through the recycle valve <NUM>.

The quantity of recycle high pressure CO<NUM> that is heated by the added heat source in heat exchanger <NUM> can be controlled by the flow control valve <NUM> and controller <NUM> (which can be characterized as a side flow heat controller). The set point of the CO<NUM> flow is controlled to minimize the temperature difference at the hot end of heat exchanger <NUM> between the high pressure CO<NUM> recycle stream <NUM> and the turbine exhaust stream at point <NUM> below <NUM>.

The discharge of condensed water together with fuel and combustion derived oxidized impurities can be controlled by maintaining a constant water level in the water separator <NUM> or in the sump of the alternative direct contact cooler. In the latter case, the excess water is discharged while the main water discharge flow is pumped through a cooling water heat exchanger and introduced into the top of the direct contact cooler above the packing layer.

With reference to <FIG>, the flow rate of oxygen to the combustor can be controlled by the flow control valve <NUM>. The set point of the flow controller can be varied to maintain a defined ratio of oxygen to fuel gas which will ensure typically <NUM>% excess oxygen above the stoichiometric value to ensure complete fuel combustion plus oxidation of any fuel derived impurities. In order to control the adiabatic flame temperature of the integral turbine combustor, it can be useful to dilute the oxygen with a quantity of CO<NUM> to produce a CO<NUM> plus O<NUM> gas mixture having between <NUM>% and <NUM>%, typically <NUM>% (molar) O<NUM> concentration. The oxygen stream can be diluted with a CO<NUM> stream taken from the inlet line of the CO<NUM> compressor <NUM>. The withdrawn CO<NUM> passes through flow control valve <NUM> and enters union <NUM> which, in some embodiments, can be a static mixer. The set point of the flow controller for valve <NUM> can be adjusted by the supervisory computer program to maintain a constant pressure at point <NUM>. The set point of the oxygen inlet flow control valve <NUM> can be adjusted to maintain a fixed ratio of oxygen to carbon dioxide flow entering the mixer <NUM>. The mixed oxidant stream passes through heater/cooler <NUM>. The cooled oxidant stream enters the oxidant compressor <NUM> where it is compressed typically to the range of about <NUM> bar to about <NUM> bar pressure. The set point of flow control valve <NUM> can be varied to control the discharge pressure of the oxidant compressor <NUM>. The oxidant compressor <NUM> can operate with fixed inlet and outlet pressures. The discharge from compressor <NUM> can be cooled to near ambient temperature in heater/cooler <NUM>. Its density is increased to the range of, for example, about <NUM>/liter to about <NUM>/liter. The dense supercritical oxidant stream <NUM> is pumped to typically <NUM> bar pressure in the multi-stage centrifugal pump <NUM>. The high pressure discharge stream exiting pump <NUM> enters the economizer heat exchanger <NUM> where it is heated by a portion of the heat released from the cooling turbine discharge stream. The flow rate of oxidant can be controlled by adjusting the speed of the oxidant pump <NUM>. The flow rate set point can be adjusted to maintain a defined ratio of oxygen to fuel gas which will provide typically <NUM>% excess oxygen above the quantity required for stoichiometric fuel gas combustion to ensure complete fuel gas combustion plus oxidation of any fuel derived impurities.

Claim 1:
A power production system comprising:
an integrated control system configured for automated control of at least one component of the power production system, the control system including at least one controller unit configured to receive an input related to a measured parameter of the power production system and configured to provide an output to the at least one component of the power production system subject to the automated control;
a turbine (<NUM>);
a power producing generator (<NUM>);
a compressor (<NUM>) downstream from the turbine (<NUM>) and in fluid connection with the turbine (<NUM>);
a pump (<NUM>) downstream from the compressor (<NUM>) and in fluid connection with the compressor (<NUM>); and
a heater (<NUM>) positioned downstream from the pump (<NUM>) and in fluid connection with the pump (<NUM>) and positioned upstream from the turbine (<NUM>) and in fluid connection with the turbine (<NUM>);
wherein the integrated control system is a
power controller (<NUM>) configured to receive an input related to power produced by the power producing generator (<NUM>) and provide an output to a heater (<NUM>) of the power production system to increase or decrease heat production by the heater (<NUM>);
wherein the integrated control system includes a pump controller (<NUM>) configured to receive an input related to temperature of an exhaust stream exiting the turbine (<NUM>) and provide an output to the pump (<NUM>) to control a flow rate of a stream passing from the pump (<NUM>) to the heater (<NUM>) and thereby control the heat output by the heater (<NUM>).