Patent Description:
Chemical refining and processing methods frequently involve converting a liquid to a vapor with a reboiler. One such example for a reboiler is a tube-in-shell steam reboiler. In the steam reboiler, steam is condensed by transferring thermal energy to a process liquid. The process liquid is vaporized by the thermal energy and returned to the process as process vapor, where, for example in a fractionation column, the vapor will interact with other molecules and separate into different components within the fractionation column.

Such a reboiler often utilizes one or more control valves to adjust the pressure or temperature of the various streams associated with the reboiler. For example, a control valve is utilized to reduce a pressure of the steam stream to limit the ultimate temperature of the steam in a heat exchanger within the reboiler. Additionally, a control valve is utilized with boiler feedwater mixed with the steam to remove any superheat. The boiler feedwater is at a much higher pressure and therefore, a control valve is needed to reduce the pressure of the boiler water, allowing it to be mixed with the steam. Furthermore, once the steam is condensed in the heat exchanger within the reboiler, a control valve is utilized with the hot condensate to modulate the duty of the reboiler.

While the reboilers achieve their intended purposes, the control valves are a source of energy loss associated with the pressure reduction of the streams. Specifically, in the control valve, mechanical energy is dissipated by the valve in a thermodynamically adiabatic, highly irreversible process. Since the energy is removed in such an irreversible process, via the pressure reduction, without recovery, the energy is lost.

Because the pressure reduction across the control valve is irreversible, it results in a lower pressure steam with greater amounts of superheat than at the inlet of the valve. For the purposes of maximizing the utility of the heat exchanger surface area, the steam should condense immediately upon entering the heat exchanger to minimize the heat exchanger surface area. With high amounts of superheat, for example greater than <NUM> degrees C, a large amount of exchanger surface area is involved in slow heat transfer of sensible heat removal from the steam. To ensure quick condensation of the steam in the heat exchanger, some water is added to the steam downstream of the control valve to minimize the steam superheat. This addition of water adds cost to the system and therefore it is desirable to be minimized or eliminated.

Returning to the energy dissipated across the control valve; this dissipated energy is often associated with energy added to the system. Thus, there is an inherent inefficiency in the process associated with supplying energy only to remove it without recovery. In the past, the cost of recovering this energy has not been justified; however, with increased mandates for improvements in energy efficiency and reduction of greenhouse gas emissions, the elimination of these oft-overlooked inefficiencies provides a means to address these new mandates. Moreover, this inefficiency is an opportunity for processors to lower operating costs and, thus increase profits.

Therefore, there is a need for an effective and efficient device and process for recovering energy from the reboiler. Additionally, it would be desirable for such devices and processes to allow processors to analyze the inefficiency of removing energy that has been added and adjust processing conditions to minimize the added energy without impacting the overall throughput of the processing/refining unit. <CIT> relates to a steam supply system for superposed turbine and process chamber, such as coal gasification. <CIT> relates to a thermal power plant, steam turbine and control method for a thermal power plant. <CIT> relates to a thermal power plant with carbon dioxide capture scrubbing equipment. <CIT> relates to carbon-dioxide-recovery-type thermal power generation system and method of operating the same.

The invention is in accordance with the appended claims. The present invention attempts to overcome one or more shortcomings associated with the conventional reboilers. Specifically, according to the present invention, the control valves in the reboilers are replaced with turbines. With turbines, the same pressure reduction is achieved by the reboiler unit. However, unlike the control valves, the turbines convert the removed energy into electrical energy that is utilized elsewhere in the processing unit and remove much of the superheat from the steam requiring less water for de-superheating. It is preferred to reduce the amount of superheat in the steam line after the turbine to less than <NUM> degrees C superheat and most preferably to less than <NUM> degrees C superheat. Thus, the turbines provide an advantage over the traditional control valves. In the reboiler described above, the turbine is able to provide information about the amount of energy removed. This information may be utilized to determine adjustments for various processing conditions which reduce the amount of energy added to the process. This permits the processor to more efficiently operate the process unit without reducing the throughput of the process unit.

The present invention may be characterized, in at least one aspect, as providing a process for recovering electrical power from a steam reboiler system with a turbine by: converting an inlet liquid process stream into a vapor phase and a liquid phase in a reboiler; heating the inlet liquid process stream within the reboiler with a stream of steam with a heat exchanger having an inlet and an outlet; reducing a pressure of the stream of steam with a turbine prior to heating the inlet liquid process stream; recovering condensate from the outlet after heating the inlet liquid process stream; rotating a turbine wheel within the turbine, the turbine wheel configured to transmit rotational movement to an electrical generator; and, generating electricity with the turbine, wherein the inlet liquid process stream is from a processing unit, and the process further comprises: receiving information from the turbine relative to an amount of electricity generated by the turbine; and, receiving information associated with a throughput of the processing unit, determining an electrical power generated target based in part upon the information associated with the throughput of the processing unit.

Also disclosed herein, but not within the scope of the present invention, there is a process for recovering electrical power from a steam reboiler with a turbine by: passing a liquid process stream to a reboiler; passing a stream of steam into a heat exchanger disposed within the reboiler; heating the liquid process stream in the reboiler with the stream of steam; recovering a stream of condensate from the heat exchanger; recovering a mixed stream from the reboiler, the mixed stream comprising the liquid process stream and a vapor portion of the liquid process stream; controlling the flow or pressure of the stream of steam with at least one turbine, the at least one turbine being disposed in a condensate recovery line, in a steam supply line, or both; and, generating electricity with the at least one turbine.

In another aspect, the present invention may be characterized as providing an apparatus for boiling a liquid stream in a reboiler. The apparatus includes a vessel with at least one inlet configured to receive a liquid process stream and at least one outlet configured to provide a mixed stream comprising the liquid process stream and a vapor portion of the liquid process stream. The apparatus further includes a heat exchanger disposed within the shell and configured to allow the liquid process stream to absorb heat from steam within the heat exchanger. Additionally, there is a condensate recovery line in communication with an outlet of the heat exchanger and a steam supply line in communication with an inlet of the heat exchanger. The apparatus includes at least one turbine comprising a turbine wheel configured to transmit rotational movement to an electrical generator, the at least one turbine being disposed in the steam supply line; and a process control system configured to receive information associated with the amount of electricity generated by the at least one turbine and to receive information associated with a throughput of the processing unit, and to determine a target electrical power generated value for the at least one turbine.

Additional aspects, embodiments, and details of the invention, all of which may be combinable in any manner, are set forth in the following detailed description of the invention.

One or more exemplary embodiments of the present invention will be described below in conjunction with the attached <FIG> which is a schematic view of a reboiler that is utilized in one or more aspects of the present invention.

As mentioned above, a reboiler with one or more turbines to recover energy from a pressure reduction is used in the various embodiments of the present invention. The energy, in the form of electrical energy is used elsewhere in the processing unit. Additionally, information associated with the amount of electrical energy produced by the turbine is used to adjust processing conditions, other than the throughput of the processing unit, to provide a more efficient operation of the processing unit.

With these general principles in mind, one or more embodiments of the present invention will be described with the understanding that the following description is not intended to be limiting.

<FIG> depicts an external reboiler system <NUM> that comprises a vessel <NUM> with at least one inlet and at least one outlet for a processing unit (not shown). A liquid process stream <NUM> is passed into the vessel <NUM>, via the inlet, and a mixed process stream <NUM>, typically a two phase mixture with a liquid portion and a vapor portion, is recovered from the vessel <NUM> via the outlet.

Inside of the vessel <NUM>, there is a heat exchanger <NUM> configured to allow for the liquid in the vessel <NUM> to absorb heat. The heat exchanger <NUM> includes an inlet <NUM> and an outlet <NUM>. In various aspects of the present invention the inlet <NUM> of the heat exchanger receives steam from a steam supply line <NUM>. The steam provides the heat energy that is transferred to the process liquid. A condensate is recovered from the heat exchanger <NUM>, via a condensate recovery line <NUM> in communication with the outlet <NUM> of the heat exchanger <NUM>. Any particular configuration for the heat exchanger <NUM> may be used to practice the present invention, so long as the heat exchanger <NUM> allows the liquid to absorb heat from the steam. For example, the heat exchanger may include one or more tubes extending within the shell <NUM>. The heat exchanger <NUM> may be internal to the vessel <NUM> (as shown) or externally connected to the vessel <NUM>.

As discussed at the outset, in conventional reboilers, before the steam is supplied to the heat exchanger <NUM>, and after the condensate is recovered from the heat exchanger <NUM>, control valves are utilized to adjust a pressure of various streams. According to the present invention, instead of using control valves, turbines <NUM>, <NUM>, <NUM> are provided in the reboiler to allow for the required pressure reductions and flow control to occur, and to recover some energy associated with the pressure reductions.

For example, in the embodiment depicted in the Figure, a turbine <NUM> is located in the steam supply line <NUM>. This turbine <NUM> lowers the pressure of the steam to avoid excess heat from being introduced in the heat exchanger <NUM>. Additionally, a boiler feedwater supply line <NUM> includes a turbine <NUM> to recover energy as the pressure of the boiler feedwater is reduced. Once the pressure of the boiler feedwater is reduced, the boiler feedwater is mixed with the steam in the steam supply line <NUM> to remove any super heat from the steam and further control the temperature of the steam supplied to the heat exchanger <NUM>. Notably, as a result of using the turbine <NUM>, as opposed to a control valve, the use of the boiler feedwater supply line <NUM> can be greatly reduced or eliminated altogether. Finally, a turbine <NUM> is also located in the condensate recovery line <NUM> in order to recover energy associated with the pressure reduction of the condensate to regulate the duty of the exchanger and pass to a lower pressure condensate recovery system. It should be appreciated that the depicted configuration of the reboiler <NUM>, with three turbines <NUM>, <NUM>, <NUM>, is intended to be exemplary in nature. Other configurations may be utilized.

The specific configuration for the turbines <NUM>, <NUM>, <NUM> is also not particularly important for the practicing of the present invention. Exemplary turbines and details of same are described in <CIT>, <CIT>, <CIT>, and <CIT>. For clarity purposes, the turbine <NUM> in the condensate recovery line <NUM> will be described with the understanding that the other turbines <NUM>, <NUM> include similar elements.

The turbines <NUM>, <NUM>, <NUM> each comprise a turbine wheel <NUM> with blades <NUM> configured to transfer, or transmit, rotational movement, created by the flow of a fluid stream passing the turbine wheel <NUM>, to an electrical generator <NUM>. The electrical generator <NUM> generally includes a first winding <NUM>, in communication with the turbine wheel <NUM> and a second winding <NUM> surrounding the first winding <NUM> and stationary with respect to the first winding <NUM>. As will be appreciated, the rotation of the first winding <NUM> creates an electrical current in the second winding <NUM>. Additionally, the turbines <NUM>, <NUM>, <NUM> may include a processor <NUM> configured to measure an amount of electricity generated by the turbine <NUM>, <NUM>, <NUM> and a transmitter <NUM> configured to transmit information associated with the amount of electricity generated by the turbine <NUM>, <NUM>, <NUM> to a computer <NUM> at a control center <NUM> for the processing unit.

Accordingly, in some embodiments, the process according to the present invention comprises directing a portion of a gaseous process stream through one or more variable-resistance turbines to control the flowrate of the gas process stream and, optionally, generate electric power therefrom; controlling a pressure and temperature of the gaseous process stream so that the gas exiting the power-recovery turbine remains in the gas phase; and measuring the flowrate or controlling the flowrate or both using a variable nozzle turbine, inlet variable guide vanes, or direct coupled variable electric load, to name a few, to vary the resistance to flow through the turbine. Again, the resistance to rotation of the variable-resistance turbine can be varied by an external variable load electric circuit which is in a magnetic field from a magnet(s) that is rotating on the turbine. As more load is put on the circuit, there is more resistance to rotation on the turbine. This in turn imparts more pressure drop across the turbine and slows the process stream flow. An algorithm in the device can also calculate the actual flow through the device by measuring the turbine RPMs and the load on the circuit. The resistance to rotation flow can also be varied by variable position inlet guide vanes. In some embodiments, the power will be generated via power-recovery turbines with variable resistance to flow made possible by either guide vanes or variable load on the electrical power generation circuit. An algorithm to calculate actual flow using the guide vanes position, power output and RPMs can be used.

If slow control response of the turbine is an issue then the use of the turbine is limited to slow responding or "loose" control point applications. A slow responding application is contemplated to have a response time to reach half way (i.e., <NUM>% of a difference) between a new (or target) steady state condition (e.g., temperature, pressure, flow rate) from an original (or starting) steady state condition when the new (or target) condition differs from the original (or stating) condition of at least <NUM>%, is of at least one second, or even greater, for example, ten seconds, at least one minute, at least ten minutes, or an hour or more, for half of the change to completed.

In the processes according to various aspects of the present invention, the process fluid is converted in the reboiler <NUM> from a liquid phase to a mixed liquid/vapor phase. The heat required for the conversion is provided by the steam in the steam supply line <NUM> to the heat exchanger <NUM>. In the heat exchanger <NUM>, the heat is absorbed from the steam by the process liquid, causing the steam to condense and the process liquid to vaporize. The condensate is recovered from the outlet <NUM> of the heat exchanger <NUM>.

Prior to passing the steam to the heat exchanger <NUM>, the pressure of the steam is reduced by passing the steam through the turbine <NUM>. Within the turbine <NUM>, the steam passing therethrough will rotate the turbine wheel <NUM> and, as is known, generate electricity via the electrical generator <NUM>. Additionally, and alternatively, the pressure of the condensate in the condensate recovery line is reduced with the turbine <NUM> which also generates electricity in the same or similar manner. Furthermore, any boiler feedwater mixed with the steam is passed through the turbine <NUM> to reduce the pressure of the boiler feedwater, also generating electricity in a same or similar manner. Unlike processes which utilize control valves for the pressure reduction, the present invention provides for the conversion of some of the energy removed via the pressure reductions to electricity.

The present invention may be implemented with a process control system. The process control system described in connection with the embodiments disclosed herein may be implemented or performed on the computer with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, or, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be a combination of computing devices, e.g., a combination of a DSP and a microprocessor, two or more microprocessors, or any other combination of the foregoing.

The steps of the processes associated with the process control system may be embodied in an algorithm contained directly in hardware, in a software module executed by a <NUM> processor, or in a combination of the two. An exemplary storage medium is in communication with the processor reading information from, and writing information to, the storage medium. This includes the storage medium being integral to or with the processor. Alternatively, the processor and the storage medium may reside as discrete components in a user terminal. These devices are merely intended to be exemplary, non-limiting examples of a computer readable storage medium. The processor and storage medium or memory are also typically in communication with hardware (e.g., ports, interfaces, antennas, amplifiers, signal processors, etc.) that allow for wired or wireless communication between different components, computers processors, or
the like, such as between the input channel, a processor of the control logic, the output channels within the control system and the operator station in the control center.

In communication relative to computers and processors refers to the ability to transmit and receive information or data. The transmission of the data or information can be a wireless transmission (for example by Wi-Fi or Bluetooth) or a wired transmission (for example using an Ethernet RJ45 cable or an USB cable). For a wireless transmission, a wireless transceiver (for example a Wi-Fi transceiver) is in communication with each processor or computer. The transmission can be performed automatically, at the request of the computers, in response to a request from a computer, or in other ways. Data can be pushed, pulled, fetched, etc., in any combination, or transmitted and received in any other manner.

According to the present invention, the process control system receives information from the turbine <NUM>, <NUM>, <NUM> relative to an amount of electricity generated by the turbine <NUM>, <NUM>, <NUM>. It is contemplated that the turbine <NUM>, <NUM>, <NUM> determines (via the processor <NUM>) the amount of electricity it has generated. Alternatively, the process control system receiving the information determines the amount of electricity that has been generated by the turbine <NUM>, <NUM>, <NUM>. In either configuration, the amount of the electricity generated by the turbine <NUM>, <NUM>, <NUM> is displayed on at least one display screen <NUM> associated with the computer <NUM> in the control center <NUM>. If the processing unit comprises a plurality of turbines <NUM>, <NUM>, <NUM>, it is further contemplated that the process control system receives information associated with the amount of electricity generated by each of the turbines <NUM>, <NUM>, <NUM>. The process control system determines a total electrical power generated based upon the information associated with the each of the turbines <NUM>, <NUM>, <NUM> and displays that the total electrical power generated on the at least one display screen <NUM>. The total electrical power generated may be displayed instead of, or in conjunction with, the amount of electrical power generated by the individual turbines <NUM>, <NUM>, <NUM>.

As discussed above, the electrical energy recovered by the turbines <NUM>, <NUM>, <NUM> is often a result of removing energy from the streams that was added to the streams in the processing unit. Thus, it is contemplated that the processes according to the present invention provide for the various processing conditions associated with the processing unit to be adjusted into order to lower the energy added to the steam(s).

For example, a simulation is run to determine the amount of harvested electrical energy available at the optimum performance for a specific unit feed and product rate. This amount of harvested electrical energy will then be the basis for reducing the flow through turbine <NUM> to the amount of steam used in the reboiler <NUM> for this same amount of feed and product at the optimum operating point.

In the present invention, the process control system receives information associated with the throughput of the processing unit, and determines a target electrical power generated value for the turbine(s) since the electricity represents energy that is typically added to the overall processing unit. The determination of the target electrical power generated value may be done when the electricity is at or near a predetermined level. In other words, if the amount of electricity produced meets or exceeds a predetermined level, the process control system can determine one or more processing conditions to adjust and lower the amount of electricity generated until it reaches the target electrical power generated value.

Thus, the process control system will analyze one or more changes to the various processing conditions associated with the processing unit to lower the amount of energy recovered by the turbines of the reboiler <NUM>. Preferably, the processing conditions are adjusted without adjusting the throughput of the processing unit. This allows for the processing unit to have the same throughput, but with a lower operating cost associated with the same throughput. The process control system may calculate and display the difference between the target electrical power generated value and the total electrical power generated on the at least one display screen <NUM>.

For example, the process control system may recognize that the total electrical power generated exceeds a predetermined level. Accordingly, the process control system may determine the target electrical power generated value. Based upon other data and information received from other sensors and data collection devices typically associated with the processing unit, the process simulation software may determine that the amount of fuel consumed in the heater associated with the steam of the reboiler can be lowered. While maintaining the throughput of the processing unit, the amount of fuel consumed in the heater is lowered. While this may lower the electricity generated by the turbine, the lower fuel consumption provides a lower operating cost for the same throughput.

Thus, not only does the present invention convert energy that is typically lost into a form that is used elsewhere in the processing unit, the processing units are provided with opportunities to lower the energy input associated with the overall processing unit and increase profits by utilizing more energy efficient processes.

It should be appreciated and understood by those of ordinary skill in the art that various other components such as valves, pumps, filters, coolers, etc. were not shown in the drawings as it is believed that the specifics of same are well within the knowledge of those of ordinary skill in the art and a description of same is not necessary for practicing or understanding the embodiments of the present invention.

Claim 1:
A process for recovering electrical power from a steam reboiler system (<NUM>) with a turbine, the process comprising:
converting an inlet liquid process stream (<NUM>) into a vapor phase and a liquid phase in a reboiler (<NUM>);
heating the inlet liquid process stream (<NUM>) within the reboiler (<NUM>) with a stream of steam (<NUM>) with a heat exchanger (<NUM>) having an inlet (<NUM>) and an outlet (<NUM>);
reducing a pressure of the stream of steam (<NUM>) with a turbine (<NUM>) prior to heating the inlet liquid process stream (<NUM>);
recovering condensate (<NUM>) from the outlet (<NUM>) after heating the inlet liquid process stream (<NUM>);
rotating a turbine wheel (<NUM>) within the turbine (<NUM>), the turbine wheel (<NUM>) configured to transmit rotational movement to an electrical generator (<NUM>); and
generating electricity with the turbine (<NUM>);
wherein the inlet liquid process stream (<NUM>) is from a processing unit; characterized in that the process further comprises:
receiving information from the turbine (<NUM>) relative to an amount of electricity generated by the turbine (<NUM>); and,
receiving information associated with a throughput of the processing unit, determining an electrical power generated target based in part upon the information associated with the throughput of the processing unit.