WO2025219271A1

WO2025219271A1 - Method for controlling boiler feed water supply for steam generation

Info

Publication number: WO2025219271A1
Application number: PCT/EP2025/060088
Authority: WO
Inventors: Muhammad Zeeshan Anwar; Srikant Vasant BADGANDI; Uma K SANKAR
Original assignee: SABIC Global Technologies BV
Current assignee: SABIC Global Technologies BV
Priority date: 2024-04-16
Filing date: 2025-04-11
Publication date: 2025-10-23
Anticipated expiration: 2026-10-16

Abstract

A method for controlling a steam production system that includes a boiler steam drum, a boiler feed water tank, at least one pump for pumping water from the boiler feed water tank to the boiler steam drum, a variable-frequency drive providing power to the pump, a flow control valve adapted to control flow of water from the boiler feed water tank, a water flow measurement unit, a pressure measurement unit upstream of the flow control valve, and a steam flow measurement unit. The method includes controlling the speed of the variable-frequency drive based on the steam flow measurement, the pressure measurement, a boiler steam drum level measurement, and/or the water flow measurement, and controlling the opening and closing of the flow control valve based on the steam flow measurement, the boiler steam drum level measurement, and/or the water flow measurement.

Description

METHOD FOR CONTROLLING BOILER FEED WATER SUPPLY FOR STEAM GENERATION

TECHNOLOGICAL FIELD

[0001] The present disclosure relates to methods and systems for controlling boiler feed water flow for a steam generation system.

BACKGROUND

[0002] Energy efficiency and greenhouse gas (GHG) reduction are among the top priorities for chemical/petrochemical companies. One of the major energy consumers in any chemical plant is the steam grid wherein natural gas is used in auxiliary boilers to produce high grade steam, which is then used in turbines to produce power. Low grade steam leaving the turbines is eventually used in reboiler heat exchangers, ejectors, and as process steam.

[0003] Watertube boilers and firetube boilers are two major types of boilers used in an industrial setting. Watertube boilers are designed to pass water through the inside of heat transfer tubes while the outside of the tubes is heated by direct contact with the hot combustion gases and through radiant heat transfer. Watertube boilers are used for a variety of applications, ranging from providing large amounts of process steam, to providing hot water or steam for space heating, to generating high-temperature, high- pressure steam for producing electricity. Firetube boilers are designed such that the hot combustion gases flow through tubes, which heat the water circulating outside of the tubes. These boilers are used primarily for space heating systems, industrial process steam, and portable power boilers. Industrial boilers can also be classified as wall-fired or tangential-fired. Wall-fired units are characterized by multiple individual burners located on a single wall or on opposing walls of the furnace, while tangential units have several rows of air and fuel nozzles located in each of the four comers of the boiler.

[0004] Boilers are supplied with water using a boiler feed water (BFW) system that includes a feed water storage tank and a pump system for supply of water to the boiler. Conventionally, the BFW header pressure is kept constant regardless of steam flow demand and low steam demand is managed either by recycling feed water back to the storage tank through a recycle valve or by pinching the valve controlling flow to the boiler to the lowest position. This can result in significant pressure energy losses in the BFW system, sometimes as much as 40% pressure energy loss, as well as significant BFW recycling (e.g., on the order of 15% recycling) due to steam load variation. Inefficiencies of this type in the BFW system contribute to GHG emissions, particularly where the pumps in the BFW system are powered by steam turbines. There remains a need in the art to enhance the efficiency of BFW supply systems to reduce natural gas consumption and GHG emissions.

BRIEF SUMMARY

[0005] To improve overall energy consumption, the present disclosure provides a boiler feed water control system and method that, in some embodiments, combines use of a variable-frequency drive adapted to provide power to the pump(s) used to pump BFW to the boiler steam drum and a four-element feed forward control loop that uses BFW flow measurement, BFW header pressure measurement, boiler steam drum level measurement, and steam flow measurement to control BFW water flow. In some embodiments, the present disclosure saves natural gas use in the boiler by replacing conventional steam turbines used to power the BFW pump(s) with electric motors. The natural gas saved in the boiler may be used to produce valuable chemicals like methanol (MeOH) or syngas. In addition, in some embodiments, BFW is pumped more efficiently with reduced pressure energy losses and reduced BFW recycle.

[0006] The present disclosure includes, without limitation, the following embodiments.

[0007] Embodiment 1 : A boiler feed water control system, comprising: a boiler steam drum adapted to produce a steam effluent stream, the boiler steam drum including a level measurement unit; a boiler feed water tank in fluid communication with the boiler steam drum via a pipeline for supplying water to the boiler steam drum; at least one pump for pumping water from the boiler feed water tank to the boiler steam drum through the pipeline; a variable-frequency drive adapted to provide power to the at least one pump; a flow control valve in the pipeline adapted to control flow rate of water from the boiler feed water tank to the boiler steam drum; a flow measurement unit in the pipeline; a pressure measurement unit in the pipeline upstream of the flow control valve; a steam flow measurement unit positioned to measure flow of the steam effluent stream; a first controller adapted to control the speed of the variable-frequency drive (and which can be a common synchronous controller adapted to control each of a plurality of separate variable-frequency drives), the controller adapted to receive one or more of a steam flow measurement from the steam flow measurement unit, a pressure measurement from the pressure measurement unit, a boiler steam drum level measurement from the level measurement unit, and a flow measurement from the flow measurement unit; and a second controller adapted to control the flow control valve, the controller adapted to receive one or more of a steam flow measurement from the steam flow measurement unit, a boiler steam drum level measurement from the level measurement unit, and a flow measurement from the flow measurement unit.

[0008] Embodiment 2: The boiler feed water control system of Embodiment 1, further comprising a speed ratio valve in the pipeline upstream of the flow control valve and adapted to adjust pressure in the pipeline upstream of the flow control valve, and a third controller adapted to control the speed ratio valve, the third controller adapted to receive a pressure measurement from the pressure measurement unit.

[0009] Embodiment 3: The boiler feed water control system of Embodiment 1 or 2, wherein the variable-frequency drive is one of a plurality of variable-frequency drives, and wherein the at least one pump comprises a plurality of pumps for pumping water from the boiler feed water tank to the boiler steam drum through the pipeline, the plurality of pumps adapted to operate in parallel, and each of the plurality of pumps driven by a separate variable-frequency drive (which can be controlled by a common synchronous controller adapted to control each of the separate variable-frequency drives). [0010] Embodiment 4: The boiler feed water control system of any one of Embodiments 1 to 3, wherein one or more of the first controller and the second controller is configured to maintain the boiler steam drum at a predetermined level, such as a level of about 30% to about 40% or about 32% to about 37%.

[0011] Embodiment 5: The boiler feed water control system of any one of Embodiments 1 to 4, wherein the third controller is configured to maintain the boiler steam drum at a predetermined level, such as a level of about 30% to about 40% or about 32% to about 37%. [0012] Embodiment 6: The boiler feed water control system of any one of Embodiments 1 to 5, wherein the first controller is configured to maintain the pressure in the pipeline upstream of the flow control valve at a predetermined level, such as a level of about 55 to about 75 bar, or about 60 to about 70 bar.

[0013] Embodiment 7: The boiler feed water control system of any one of Embodiments 1 to 6, wherein the third controller is configured to maintain pressure in the pipeline upstream of the flow control valve at a predetermined level, such as a level of about 55 to about 75 bar, or about 60 to about 70 bar.

[0014] Embodiment 8: A method for controlling boiler feed water supply for a steam production system, comprising: providing a steam production system comprising a boiler steam drum adapted to produce a steam effluent stream, the boiler steam drum including a level measurement unit; a boiler feed water tank in fluid communication with the boiler steam drum via a pipeline for supplying water to the boiler steam drum; at least one pump for pumping water from the boiler feed water tank to the boiler steam drum through the pipeline; a variable-frequency drive adapted to provide power to the at least one pump; a flow control valve in the pipeline adapted to control flow of water from the boiler feed water tank to the boiler steam drum; a flow measurement unit in the pipeline; a pressure measurement unit in the pipeline upstream of the flow control valve; and a steam flow measurement unit positioned to measure flow of the steam effluent stream; controlling the speed of the variable-frequency drive based on one or more of a steam flow measurement from the steam flow measurement unit, a pressure measurement from the pressure measurement unit, a boiler steam drum level measurement from the level measurement unit, and a flow measurement from the flow measurement unit; and controlling the opening and closing of the flow control valve based on one or more of a steam flow measurement from the steam flow measurement unit, a boiler steam drum level measurement from the level measurement unit, and a flow measurement from the flow measurement unit.

[0015] Embodiment 9: The method of Embodiment 8, wherein the steam production system further comprises a speed ratio valve in the pipeline upstream of the flow control valve, the method further comprising controlling the opening and closing of the speed ratio valve based on a pressure measurement from the pressure measurement unit. [0016] Embodiment 10: The method of Embodiment 8 or 9, wherein the at least one pump further comprises a plurality of pumps for pumping water from the boiler feed water tank to the boiler steam drum through the pipeline, and wherein the variablefrequency drive is one of a plurality of variable-frequency drives, the plurality of pumps adapted to operate in parallel, and each of the plurality of pumps driven by a separate one of the plurality of variable-frequency drives, and wherein controlling the speed of the variable-frequency drive comprises controlling each of the plurality of variable-frequency drives, optionally through a common synchronous controller adapted to control each of the plurality of variable-frequency drives.

[0017] Embodiment 11 : The method of any one of Embodiments 8 to 10, wherein controlling of the speed of the variable-frequency drive and/or controlling the opening and closing of the flow control valve maintains the boiler steam drum at a predetermined level, such as a level of about 30% to about 40% or about 32% to about 37%.

[0018] Embodiment 12: The method of any one of Embodiments 8 to 11, wherein controlling the opening and closing of the speed ratio valve maintains the boiler steam drum at a predetermined level, such as a level of about 30% to about 40% or about 32% to about 37%.

[0019] Embodiment 13: The method of any one of Embodiments 8 to 12, wherein controlling of the speed of the variable-frequency drive maintains the pressure in the pipeline upstream of the flow control valve at a predetermined level, such as a level of about 55 to about 75 bar, or about 60 to about 70 bar.

[0020] Embodiment 14: The method of any one of Embodiments 8 to 13, wherein controlling the opening and closing of the speed ratio valve maintains pressure in the pipeline upstream of the flow control valve at a predetermined level, such as a level of about 55 to about 75 bar, or about 60 to about 70 bar.

[0021] Embodiment 15: The method of any one of Embodiments 8 to 14, characterized by one or more of the following: less than 5% by weight of water leaving the at least one pump is recycled back to the boiler feed water tank, such as less than 4%, or less than 3%, or less than 2%, or less than 1%; and pressure energy losses across the flow control valve are less than 25%, such as less than 20%, or less than 15%. [0022] These and other features, aspects, and advantages of the present disclosure will be apparent from a reading of the following detailed description together with the accompanying figures, which are briefly described below. The present disclosure includes any combination of two, three, four or more features or elements set forth in this disclosure, regardless of whether such features or elements are expressly combined or otherwise recited in a specific example implementation described herein. This disclosure is intended to be read holistically such that any separable features or elements of the disclosure, in any of its aspects and example implementations, should be viewed as combinable, unless the context of the disclosure clearly dictates otherwise.

[0023] It will therefore be appreciated that this Brief Summary is provided merely for purposes of summarizing some example implementations so as to provide a basic understanding of some aspects of the disclosure. Accordingly, it will be appreciated that the above described example implementations are merely examples and should not be construed to narrow the scope or spirit of the disclosure in any way. Other example implementations, aspects and advantages will become apparent from the following detailed description taken in conjunction with the accompanying figures which illustrate, by way of example, the principles of some described example implementations.

BRIEF DESCRIPTION OF THE FIGURES

[0024] Having thus described aspects of the disclosure in the foregoing general terms, reference will now be made to the accompanying figure, which is not necessarily drawn to scale, and wherein:

[0025] FIG. l is a schematic representation of a BFW supply system for controlling BFW flow to a boiler steam drum.

DETAILED DESCRIPTION

[0026] Some implementations of the present disclosure will now be described more fully hereinafter with reference to the accompanying figures, in which some, but not all implementations of the disclosure are shown. Indeed, various implementations of the disclosure may be embodied in many different forms and should not be construed as limited to the implementations set forth herein; rather, these example implementations are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Like reference numerals refer to like elements throughout.

[0027] Unless specified otherwise or clear from context, references to first, second or the like should not be construed to imply a particular order. A feature described as being above another feature (unless specified otherwise or clear from context) may instead be below, and vice versa; and similarly, features described as being to the left of another feature else may instead be to the right, and vice versa. Also, while reference may be made herein to quantitative measures, values, geometric relationships or the like, unless otherwise stated, any one or more if not all of these may be absolute or approximate to account for acceptable variations that may occur, such as those due to engineering tolerances or the like.

[0028] All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other (e.g., ranges of “up to 25%, or, more specifically, 5% to 20%”, is inclusive of the endpoints and all intermediate values of the ranges of “5% to 25%, ” etc.). “Combination” is inclusive of blends, mixtures, alloys, reaction products, and the like.

[0029] As used herein, unless specified otherwise or clear from context, the “or” of a set of operands is the “inclusive or” and thereby true if and only if one or more of the operands is true, as opposed to the “exclusive or” which is false when all of the operands are true. Thus, for example, “[A] or [B]” is true if [A] is true, or if [B] is true, or if both [A] and [B] are true. Further, the articles “a” and “an” mean “one or more,” unless specified otherwise or clear from context to be directed to a singular form.

[0030] The present disclosure relates to a method and system for controlling BFW flow within a steam generation system to improve efficiency with a four element control system. Steam is typically generated from auxiliary boilers, which is then fed to a plurality of steam headers. Headers at different pressures provide the steam requirements of various turbines, heat exchangers, process steam, ejectors, and the like within the chemical plant supported by the steam system.

[0031] In some embodiments, the present disclosure improves energy efficiency through use of electric motors to power one or more pumps that convey BFW to a boiler. Conventionally, such pumps are powered by steam-driven turbines, which have an overall cycle efficiency of only about 25% in condensing mode or alternatively produce low pressure steam that can go unused in the system. Electric motors have a significantly higher overall cycle efficiency based on the thermal power plant efficiency, such as about 35%.

[0032] Additionally, conventional steam generation systems typically operate at a constant BFW header pressure, which can lead to huge pressure losses within the BFW supply system due to severe constriction of the BFW control valve and/or significant recycling of BFW back to the BFW storage tank to compensate for variability in steam demand within the system. In these systems, steam is typically produced from burning fuel such as natural gas in the boilers, which is a significant contributor to GHG emissions of the chemical plant, and inefficiencies in the BFW supply loop as described above lead to additional energy losses.

[0033] With electrification of the BFW pumps, BFW supply system inefficiencies can be improved through use of synchronous variable-frequency drives (VFDs) to power the BFW pumps and adding a feed water pressure control loop as a fourth element by using a feedforward strategy in boiler level control to manage the speed of VFDs controlled by changes in steam flow rate. In some embodiments, the control loop will use four elements for control: BFW flow measurement, BFW header pressure measurement, boiler steam drum level measurement, and steam flow measurement.

[0034] In some embodiments, the feedforward feed water pressure control strategy uses BFW header pressure and steam flow rate measurements to control the set point of the VFD speed controller to maintain the pressure upstream of a feed water valve. In this way, speed of the pumps can be adjusted to match the steam flow and demand. Changes in steam flow rate demand can be almost immediately counteracted by similar changes in VFD speed and feed water flow rate. To ensure that deviations in boiler steam drum level are also used for control, the output of a boiler steam drum level controller is added to the feedforward control loop receiving the steam flow measurement and subsequently is added to the BFW pressure controller.

[0035] The combination of drum level measurement, steam flow measurement, feed flow measurement and BFW header pressure measurement to control boiler drum level provides four-element control of BFW flow. In some embodiments, this four-element process control scheme uses a speed ratio valve upstream of the BFW valve for primary control of drum level with secondary cascade control loops of steam flow. This will enable the BFW system to operate at an efficient pressure and reduce or eliminate pressure energy losses in the BFW system and/or reduce or eliminate recycling of BFW due to steam load variation. In some embodiments, this four-element process control scheme uses a speed ratio valve at upstream of the BFW valve for primary control of drum level with secondary cascade control loops of steam flow, enabling the BFW system operating at optimum pressure and there-by reducing pressure energy losses in the BFW system along-with unwanted re-cycling of Boiler Feed Water (BFW). This will result in optimum operation of the BFW system.

[0036] Surprisingly, the inventor discovered by using the four-element process control which uses a speed ratio valve that showed better process control and advantage while operating the BFW with an efficient pressure and reduced energy loses which is not possible to achieve from a conventional valve system.

[0037] In some embodiments, the present disclosure results in reduced steam consumption from boilers, and electricity demand optimization of BFW electric drives, by optimizing the BFW header pressure, thereby resulting in reduced fuel firing in the boiler section and optimized electricity consumption by the pumps. The saved fuel, which could be natural gas or hydrogen, can be used as a feedstock for producing valuable chemicals like methanol, ammonia, or purified hydrogen. This reduced fuel and electricity consumption can lead to significant reduction in GHG emissions, which aids in decarbonization efforts.

[0038] The controllers referenced herein can vary, but will typically include a processor. The processor can include at least one processor core, microprocessor, coprocessor, or various other computing or processing devices including one or more integrated circuits such as, for example, an ASIC (application specific integrated circuit), an FPGA (field programmable gate array), some combination thereof, or the like. In some examples, the processing circuitry may include memory coupled to or integrated with the processor, and which may store data, computer program instructions executable by the processor, some combination thereof, or the like. In some example embodiments, the processor can be configured to execute instructions that can be stored in the memory or that can be otherwise accessible to the processor. As such, whether configured by hardware or by a combination of hardware and software, the processor is capable of performing operations according to various embodiments noted herein.

[0039] FIG. 1 schematically illustrates an embodiment of a BFW supply system 10 according to an embodiment of the present disclosure. As shown, the BFW supply system 10 includes a BFW storage tank 20, typically a deaerator tank, in fluid communication with a boiler steam drum 30 for supplying water for the production of steam via a pipeline 25. The BFW storage tank 20 can include one or more deaerator valves that release gas pressure build-up within the tank. In some embodiments, steam produced in the boiler steam drum 30 passes through a superheater 35 as a steam effluent stream and enters a steam header system. In some embodiments, the BFW passes through an economizer 40, which is a heat exchanger adapted to preheat the water, before entering the boiler steam drum 30. Flow through the BFW supply system 10 is at least partially controlled using a flow control valve 60, and advantageously also through a speed ratio valve 65, as explained below.

[0040] Steam in the steam effluent stream, which is produced in the boiler steam drum 30, is typically fed to a high pressure steam header (not shown). In some embodiments, the high pressure steam header will operate at a temperature in the range of about 300 to about 550 °C, such as about 350 to about 475 °C, and at a pressure in the range of about 35 to about 125 bar, such as about 40 to about 110 bar or about 40 bar to about 50 bar.

[0041] In some embodiments, water is conveyed through the BFW supply system 10 using one or more pumps 45, which are advantageously powered by variable-frequency drives (VFDs) 50 adapted to provide power to the pumps. As would be understood, a VFD is a drive system comprising an AC electric motor and a controller that controls the speed and torque of the electric motor. The AC electric motor is typically a three-phase induction motor or synchronous motor and the VFD controller is typically a solid-state power conversion system that converts AC line input to AC inverter output. The number of pumps/VFDs is not limiting, but there are typically a plurality of pumps/VFDs, such as 2 or 3 pumps/VFDs. To maximize efficiency of the electric motors, a common synchronous controller 55 can be used to control all of the pumps/VFDs to help reduce or eliminate unloading of individual pumps (i.e., requiring reduction of electric motor rpm) in order to maintain the same total throughput of the pumps. In some embodiments, the synchronous controller 55 can be used to adjust downstream header pressure and other system parameters with relatively small changes in VFD speed, which is typically in the range of about 3200 to about 3800 rpm.

[0042] For any additional steam from the boilers required, BFW flow rate to be fed into the steam drum at a given set pressure of BFW supply is controlled by the BFW pump speed. The synchronous controller function is set to operate the VFD of each BFW pump in parallel operation to maintain the pressure of the BFW header pressure at a given set point by ramping up the BFW pumps’ rpm simultaneously to avoid surge in BFW flow or potential unloading of the pumps.

[0043] As noted previously, in some embodiments, control of the BFW supply system 10 is accomplished using a four-element feedforward control scheme. The four elements used for control are: BFW header pressure measured using pressure measurement unit such as a pressure sensor 70 located upstream of the flow control valve 60; BFW header flow rate measured using a flow measurement unit such as a flow rate sensor 75; boiler steam drum 30 level measured using a level measurement unit 80; and steam flow rate measured using a steam flow measurement unit such as a steam flow rate sensor 85. The types of measurement units are not limiting and can be any sensor known in the art. Example flow sensors include differential pressure flow sensors, thermal mass flow sensors, mechanical flow sensors, electromagnetic flow sensors, and the like. Example pressure sensors include potentiometric pressure sensors, inductive pressure sensors, capacitive pressure sensors, piezoelectric pressure sensors, strain gauge pressure sensors, and the like. Example level measurement units include hydrostatic sensors, ultrasonic sensors, radar sensors, float sensors, capacitive sensors, and the like.

[0044] The various measurements noted above are used as input data for various controllers within the BFW supply system 10. In the illustrated embodiment of FIG. 1, all four of the primary measurement points (drum level measurement, steam flow measurement, feed flow measurement, and BFW header pressure measurement) are input data for the synchronous controller 55 adapted to control operation of the variable- frequency drives 50. The synchronous controller 55 can adjust the speed of the variablefrequency drives 50 in response to change in the measurements noted above. In particular, the synchronous controller 55 can use adjustments in the speed of the variablefrequency drives 50 to maintain one or both of the level of the boiler steam drum 30 at a predetermined setpoint and the pressure in the pipeline 25 upstream of the flow control valve 60 at a predetermined setpoint. For example, the synchronous controller 55 can help maintain the boiler steam drum 30 at a predetermined level, such as a level of about 30% to about 40% or about 32% to about 37%. In addition, the synchronous controller 55 can help maintain the pressure in the pipeline 25 upstream of the flow control valve 60 at a predetermined level, such as a level of about 55 to about 75 bar, or about 60 to about 70 bar.

[0045] In some embodiments, a feed flow controller 90 is adapted to control the flow control valve 60 using one or more of steam flow measurement from the steam flow rate sensor 85, a boiler steam drum level measurement from the level measurement unit 80, and a flow measurement from the flow rate sensor 75. In the embodiment illustrated, the feed flow controller 90 receives data from all three sensors/measurement units.

[0046] As noted above, the BFW supply system 10 can further include a speed ratio valve 65 in the pipeline 25 upstream of the flow control valve 60 and adapted to adjust pressure in the pipeline upstream of the flow control valve, and a pressure controller 95 adapted to control the speed ratio valve. In this manner, the flow control valve 60 is primarily responsible for changing water flow rate, while the speed of the variablefrequency drives 50 and the position of the speed ratio valve 65 maintain the pipeline 25 at the desired pressure. The pressure controller 95 can receive a pressure measurement from the pressure sensor 70. The opening and closing of the speed ratio valve 65 is based on the pressure measurement from the pressure sensor 70. Adjustment of the speed ratio valve 65 can help maintain pressure in the pipeline 25 upstream of the flow control valve 60 at a predetermined level, such as a level of about 55 to about 75 bar, or about 60 to about 70 bar. In some embodiments, it can be advantageous to use the speed ratio valve 65 to maintain pressure in the pipeline 25 upstream of the flow control valve 60 at a pressure set point that is about 10 to about 12 bar higher than the pressure in the boiler steam drum 30, which is measured using a pressure sensor (not shown). This pressure is indirectly controlled by the BFW header pressure as such boiler steam drum pressure sensor is not involved in the level control loop of the steam drum. In addition, adjustment of the speed ratio valve 65 can help maintain the boiler steam drum 30 at a predetermined level, such as a level of about 30% to about 40% or about 32% to about 37%.

[0047] In some embodiments, the BFW supply system 10 of the present disclosure can provide enhanced efficiency by, for example, reducing or eliminating the recycling of water back to the BFW storage tank 20 through a valve 100 and/or reducing or eliminating pressure energy losses due to severe constriction in the flow control valve 60. In some embodiments, less than 5% by weight of water leaving the one or more pumps 45 is recycled back to the BFW storage tank 20, such as less than 4%, or less than 3%, or less than 2%, or less than 1% (e.g. 0 to about 5% or 1 to about 5%). In some embodiments, pressure energy losses across the flow control valve 60 (i.e., change in pressure from upstream to downstream of the flow control valve) are less than 25%, such as less than 20%, or less than 15% (e.g., about 5 to about 25% or about 7.5 to about 15%).

EXPERIMENTAL

[0048] The BFW supply system of FIG. 1 was modeled in Aspen Plus V-10 and compared to a similar system using steam-powered turbines to provide power to the pumps instead of electric motors and using three-element control with no speed ratio valve or BFW header pressure measurement. The system of FIG. 1 provides the following benefits relative to the comparative system:

[0049] (1) overall reduction in energy consumption of about 0.3 to about 0.5 M-

MMBTU/Yr depending on the source of power (natural gas fuel burning or renewable); [0050] (2) net CO2 emissions reduction of about 10 - 25 KTA depending on the source of power (fuel burning or renewable); and

[0051] (3) generation of additional methanol equivalent to 10 - 20 KTA, if saved natural gas is used for methanol production.

[0052] In general, the invention may alternately comprise, consist of, or consist essentially of, any appropriate components herein disclosed. The invention may additionally, or alternatively, be formulated so as to be devoid, or substantially free, of any components, materials, ingredients, adjuvants or species used in the prior art compositions or that are otherwise not necessary to the achievement of the function and/or objectives of the present invention. [0053] Many modifications and other implementations of the disclosure will come to mind to one skilled in the art to which this disclosure pertains having the benefit of the teachings presented in the foregoing descriptions and the associated figures. Therefore, it is to be understood that the disclosure is not to be limited to the specific implementations disclosed herein and that modifications and other implementations are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

WHAT IS CLAIMED IS:

1. A boiler feed water control system, comprising:

(a) a boiler steam drum adapted to produce a steam effluent stream, the boiler steam

5 drum including a level measurement unit;

(b) a boiler feed water tank in fluid communication with the boiler steam drum via a pipeline for supplying water to the boiler steam drum;

(c) at least one pump for pumping water from the boiler feed water tank to the boiler steam drum through the pipeline;

10 (d) a variable-frequency drive adapted to provide power to the at least one pump;

(e) a flow control valve in the pipeline adapted to control flow rate of water from the boiler feed water tank to the boiler steam drum;

(f) a flow measurement unit in the pipeline;

(g) a pressure measurement unit in the pipeline upstream of the flow control valve;

(h) a steam flow measurement unit positioned to measure flow of the steam effluent stream;

(i) a first controller adapted to control the speed of the variable-frequency drive, the controller adapted to receive one or more of a steam flow measurement from the steam flow measurement unit, a pressure measurement from the pressure

20 measurement unit, a boiler steam drum level measurement from the level measurement unit, and a flow measurement from the flow measurement unit; and

(j) a second controller adapted to control the flow control valve, the controller adapted to receive one or more of a steam flow measurement from the steam flow measurement unit, a boiler steam drum level measurement from the level measurement unit, and a flow measurement from the flow measurement unit.

2. The boiler feed water control system of claim 1, further comprising a speed ratio valve in the pipeline upstream of the flow control valve and adapted to adjust pressure in the pipeline upstream of the flow control valve, and a third controller

30 adapted to control the speed ratio valve, the third controller adapted to receive a pressure measurement from the pressure measurement unit.

3. The boiler feed water control system of claim 1, wherein the variable-frequency drive is one of a plurality of variable-frequency drives, and wherein the at least one pump comprises a plurality of pumps for pumping water from the boiler feed water tank to the boiler steam drum through the pipeline, the plurality of pumps adapted to operate in parallel, and each of the plurality of pumps driven by a separate variable-frequency drive.

4. The boiler feed water control system of claim 1, wherein one or more of the first controller and the second controller is configured to maintain the boiler steam drum at a predetermined level, such as a level of about 30% to about 40% or about 32% to about 37%.

5. The boiler feed water control system of claim 2, wherein the third controller is configured to maintain the boiler steam drum at a predetermined level, such as a level of about 30% to about 40% or about 32% to about 37%.

6. The boiler feed water control system of claim 1, wherein the first controller is configured to maintain the pressure in the pipeline upstream of the flow control valve at a predetermined level, such as a level of about 55 to about 75 bar, or about 60 to about 70 bar.

7. The boiler feed water control system of claim 2, wherein the third controller is configured to maintain pressure in the pipeline upstream of the flow control valve at a predetermined level, such as a level of about 55 to about 75 bar, or about 60 to about 70 bar.

8. A method for controlling boiler feed water supply for a steam production system, comprising: i) providing a steam production system comprising a boiler steam drum adapted to produce a steam effluent stream, the boiler steam drum including a level measurement unit; a boiler feed water tank in fluid communication with the boiler steam drum via a pipeline for supplying water to the boiler steam drum; at least one pump for pumping water from the boiler feed water tank to the boiler steam drum through the pipeline; a variable-frequency drive adapted to provide power to the at least one pump; a flow control valve in the pipeline adapted to control flow of water from the boiler feed water tank to the boiler steam drum; a flow measurement unit in the pipeline; a pressure measurement unit in the pipeline upstream of the flow control valve; and a steam flow measurement unit positioned to measure flow of the steam effluent stream; ii) controlling the speed of the variable-frequency drive based on one or more of a steam flow measurement from the steam flow measurement unit, a pressure measurement from the pressure measurement unit, a boiler steam drum level measurement from the level measurement unit, and a flow measurement from the flow measurement unit; and iii) controlling the opening and closing of the flow control valve based on one or more of a steam flow measurement from the steam flow measurement unit, a boiler steam drum level measurement from the level measurement unit, and a flow measurement from the flow measurement unit.

9. The method of claim 8, wherein the steam production system further comprises a speed ratio valve in the pipeline upstream of the flow control valve, the method further comprising controlling the opening and closing of the speed ratio valve based on a pressure measurement from the pressure measurement unit.

10. The method of claim 8, wherein the at least one pump further comprises a plurality of pumps for pumping water from the boiler feed water tank to the boiler steam drum through the pipeline, and wherein the variable-frequency drive is one of a plurality of variable-frequency drives, the plurality of pumps adapted to operate in parallel, and each of the plurality of pumps driven by a separate one of the plurality of variable-frequency drives, and wherein controlling the speed of the variable-frequency drive comprises controlling each of the plurality of variable-frequency drives, optionally through a common synchronous controller adapted to control each of the plurality of variable-frequency drives.

11. The method of claim 8, wherein controlling of the speed of the variable-frequency drive and/or controlling the opening and closing of the flow control valve maintains the boiler steam drum at a predetermined level, such as a level of about 30% to about 40% or about 32% to about 37%.

12. The method of claim 9, wherein controlling the opening and closing of the speed ratio valve maintains the boiler steam drum at a predetermined level, such as a level of about 30% to about 40% or about 32% to about 37%.

13. The method of claim 8, wherein controlling of the speed of the variable-frequency drive maintains the pressure in the pipeline upstream of the flow control valve at a predetermined level, such as a level of about 55 to about 75 bar, or about 60 to about 70 bar.

14. The method of claim 9, wherein controlling the opening and closing of the speed ratio valve maintains pressure in the pipeline upstream of the flow control valve at a predetermined level, such as a level of about 55 to about 75 bar, or about 60 to about 70 bar.

15. The method of any one of claims 8 to 14, characterized by one or more of the following:

(a) less than 5% by weight of water leaving the at least one pump is recycled back to the boiler feed water tank, such as less than 4%, or less than 3%, or less than 2%, or less than 1%; and

(b) pressure energy losses across the flow control valve are less than 25%, such as less than 20%, or less than 15%.