Direct conversion gas making process optimization method for adjusting combustion air feeding amount of square box furnace

Abstract

A direct-conversion gas-making process optimization method for adjusting the combustion air feeding amount of a square-box furnace comprises the steps of obtaining a direct-conversion gas-making process flow, extracting current combustion data of the square-box furnace, conducting current reference state evaluation on the direct-conversion gas-making process flow, adjusting the combustion air feeding amount of the square-box furnace based on current fuel gas feeding, and optimizing the combustion air feeding amount of the square-box furnace. A trend chart of the flue gas residual oxygen amount, the air feeding amount, the fuel gas feeding amount and the combustion heat release amount is constructed; and drawing a flue gas residual oxygen amount, air feeding amount, fuel gas variation amount, byproduct steam variation amount and annual operation cost saving amount variation trend chart corresponding to the first strategy and the second strategy, and determining an economic optimal strategy under different flue gas residual oxygen amount targets and the air feeding amount, the fuel gas variation amount and the byproduct steam variation amount corresponding to the economic optimal strategy.

Description

Technical Field

[0001] The invention relates to the technical field of direct-rotation gasification technology, and in particular to a direct-rotation gasification technology optimization method for adjusting the combustion air feed amount of a square box furnace. Background Art

[0002] In the industrial direct gasification process, the box furnace is the core equipment of a conversion process, and its combustion efficiency directly affects the energy and resource utilization of the entire process. For the combustion of natural gas, the ideal flue gas residual oxygen content should usually be maintained between 3-5%. This range can ensure the full combustion of the fuel and improve the thermal efficiency. In the current combustion system, the flue gas residual oxygen content is often higher than the ideal level, and there is an excessive amount of combustion air feed. This inappropriate feed will reduce the combustion thermal efficiency and cause unnecessary energy or resource waste.

[0003] The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art. Summary of the invention

[0004] In view of the problems existing in the prior art, the present invention proposes a direct-conversion gasification process optimization method for adjusting the combustion air feed amount of a square box furnace, which clearly and intuitively displays the difference between the current flue gas residual oxygen content and the ideal level, clarifies the theoretical combustion air feed amount under different flue gas residual oxygen content targets, and provides two feasible energy-saving optimization paths aimed at improving the energy or resource utilization efficiency of the system by increasing by-product steam or reducing fuel gas consumption. It determines the optimization strategy with higher annual operating cost savings under the established flue gas residual oxygen content target and the corresponding key parameters such as theoretical air feed amount, fuel gas change, by-product steam change, etc., thereby achieving better energy saving and environmental protection.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for optimizing a direct-conversion gasification process for adjusting the combustion air feed amount of a square box furnace comprises:

[0007] S100: Obtain the direct-to-gasification process flow, extract the current combustion data of the square box furnace, conduct a current baseline status assessment of the direct-to-gasification process, and build an Aspen Plus simulation model;

[0008] S200: Based on the current fuel gas feed, the air feed rate of the square box furnace is adjusted in the Aspen Plus simulation model to construct the flue gas residual oxygen content and air feed rate (F air ), fuel gas feed rate (F fuel ) and combustion heat (Q total ) trend chart;

[0009] S300: Based on the trend graph, obtain the current fuel gas feed rate and the current square box furnace heat demand and the air feed rate under the process gas preheater heat load and the boiler feed water preheater heat load with the flue gas residual oxygen content change trend, and record it as the first strategy; extract the thermal enthalpy of the by-product steam of the direct conversion process, and based on the boiler feed water preheater heat load change trend with the flue gas residual oxygen content, obtain the change of the by-product steam of the direct conversion gasification process under different flue gas residual oxygen contents; obtain the unit price of the by-product steam, and calculate the annual operating cost savings brought by the change of the by-product steam along with the flue gas residual oxygen content change trend;

[0010] S400, obtaining the combustion calorific value of the fuel natural gas, obtaining the current boiler feed water preheater heat load and the current square box furnace heat demand and the air feed amount and the fuel gas feed change amount under the process gas preheater heat load with the flue gas residual oxygen content change trend based on the trend chart, and recording it as the second strategy; obtaining the fuel gas unit price, calculating the annual operating cost savings brought by saving fuel gas with the flue gas residual oxygen content change trend;

[0011] S500: Draw a trend chart of flue gas residual oxygen content, air feed rate, fuel gas change, by-product steam change, and annual operating cost savings corresponding to the first strategy and the second strategy, and determine the economically optimal strategy under different flue gas residual oxygen content targets and its corresponding air feed rate, fuel gas change, and by-product steam change.

[0012] In the direct-conversion gasification process optimization method for adjusting the combustion air feed amount of the square box furnace, in step S100, in the direct-conversion gasification process, the natural gas and steam mixture are respectively sent to the square box first-stage furnace and the heat exchange converter, and the two first-stage conversion gases are merged and enter the second-stage furnace. The heat source of the square box furnace is the combustion fuel gas, and the heat source of the heat exchange converter is the high-temperature second-stage conversion gas; the fuel gas is sent to the convection section coil of the first-stage converter and heated, and then used as fuel for the top burner and auxiliary burner of the square box converter. The flue gas from the first-stage converter enters the convection section to preheat the raw gas, fuel gas and air process gas and preheat the boiler feed water to produce by-product steam, and finally goes to the induced draft fan for discharge at the designed flue gas exhaust temperature.

[0013] In the direct-conversion gasification process optimization method for adjusting the combustion air feed amount of a square box furnace, in step S100, the extracted current combustion data of the square box furnace includes fuel gas feed amount, air feed amount, combustion heat release and flue gas residual oxygen content; the current benchmark state assessment of the direct-conversion gasification process includes assessing the heat requirement of the first stage conversion, the heat load of each process gas preheater, the heat load of the boiler feed water preheater and the designed flue gas temperature.

[0014] In the direct-conversion gasification process optimization method for adjusting the combustion air feed amount of the square box furnace, in step S200, the current fuel gas feed is maintained unchanged, and the combustion air feed amount of the square box furnace is gradually adjusted to obtain the change trend of the flue gas residual oxygen content and the total combustion heat release under different fuel air feed amounts.

[0015] In the direct conversion gasification process optimization method for adjusting the air feed amount of the square box furnace combustion, in step S300, in the first strategy, the air feed amount under different flue gas residual oxygen contents is expressed as: air，策略1 =F air , where F air，第一策略 represents the air feed rate in the first strategy, and the heat load of the boiler feed water preheater under different flue gas residual oxygen contents is expressed as:

[0016]

[0017] Where Q3 represents the heat load of the boiler feed water preheater; Qtota l represents the total heat released by combustion; Q1 represents the heat required for the first stage of conversion; Q2 represents the heat load of the process gas preheater; the superscript ini represents the current value; the change in the by-product steam under different flue gas residual oxygen content is expressed as:

[0018]

[0019] Where, ΔF steam Indicates the change in by-product steam; h steam represents the steam enthalpy; the annual operating cost savings under different flue gas residual oxygen content are expressed as:

[0020] ΔCo1=ΔF steam ·c steam

[0021] Where ΔCo1 represents the annual operating cost savings of the first strategy; C steam Indicates the unit price of steam.

[0022] In the direct conversion gasification process optimization method for adjusting the combustion air feed amount of the square box furnace, in step S400, in the second strategy, the air feed amount under different flue gas residual oxygen contents is expressed as:

[0023]

[0024] Among them, F air，第二策略 is the air feed amount in the second strategy.

[0025] In the direct conversion gasification process optimization method for adjusting the combustion air feed amount of the square box furnace, in step S400, in the second strategy, the change in fuel gas feed under different flue gas residual oxygen contents is expressed as:

[0026]

[0027] Where, ΔF fuel Indicates the change in fuel gas; q fuel Indicates the calorific value of fuel gas combustion.

[0028] In the direct conversion gasification process optimization method for adjusting the combustion air feed amount of the square box furnace, in step S400, in the second strategy, the annual operating cost savings under different flue gas residual oxygen contents are expressed as:

[0029] ΔCo2=ΔF fuel ·c fuel , where ΔCo2 represents the annual operating cost savings of the second strategy; c fuel Indicates the unit price of natural gas fuel.

[0030] In the direct-conversion gasification process optimization method for adjusting the air feed amount of the square box furnace combustion, in step S500, the residual oxygen content in the flue gas is used as the horizontal axis, and the air feed amount, the change in fuel gas, the change in by-product steam and the annual operating cost savings are used as the vertical axis to draw the trend graphs of the residual oxygen content in the flue gas, the air feed amount, the change in fuel gas, the change in by-product steam and the annual operating cost savings corresponding to the first strategy and the second strategy respectively.

[0031] In the direct-conversion gasification process optimization method for adjusting the air feed amount of the square box furnace combustion, for a given target residual oxygen content, the annual operating cost savings corresponding to the first strategy and the second strategy are respectively determined based on the flue gas residual oxygen content, air feed amount, fuel gas change, by-product steam change, and annual operating cost savings change trend chart: if ΔCo1>ΔCo2, the first strategy is the more economical energy-saving scheme, the fuel gas consumption remains unchanged, the by-product steam amount changes, and the air feed amount and by-product steam change at the target residual oxygen content are obtained from the trend chart; if ΔCo1<ΔCo2, the second strategy is the more economical energy-saving scheme, the by-product steam amount remains unchanged, the fuel gas consumption changes, and the air feed amount and fuel gas change at the target residual oxygen content are obtained from the trend chart.

[0032] Compared with the prior art, the present invention has the following advantages:

[0033] The present invention extracts the process parameters of the current direct-conversion gasification process, obtains parameters such as flue gas residual oxygen content and combustion heat release under different air feed rates, and then respectively takes increasing byproduct steam and saving fuel gas as energy-saving optimization strategies, determines the air feed rate, fuel gas change, byproduct steam change and annual operating cost savings corresponding to the two energy-saving optimization paths along with the flue gas residual oxygen content change trend, and accordingly determines the energy-saving optimization path with the largest annual operating cost savings under the target flue gas residual oxygen content as the optimal energy-saving optimization strategy, and its corresponding theoretical air feed rate, fuel gas change, byproduct steam change and annual operating cost savings and other key parameters. The optimization of air feed rate and increasing byproduct steam / saving fuel gas consumption is of great significance to improving the thermal efficiency of the square box furnace and the energy / resource utilization efficiency of the direct-conversion gasification process. The present disclosure can also be extended to direct-conversion gasification systems using other fuel types, establish a correlation between flue gas residual oxygen content and fuel-air ratio, analyze the potential for improving system energy or resource utilization efficiency under target residual oxygen content, and in actual production, combined with automatic monitoring and control systems, achieve real-time adjustment of the square box furnace feed air volume and efficient utilization of system energy resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] By reading the detailed description of the preferred specific embodiments below, various other advantages and benefits of the present invention will become clear to those of ordinary skill in the art. The drawings in the specification are only for the purpose of illustrating the preferred embodiments and are not considered to be limitations of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without creative work. Moreover, the same reference numerals are used to represent the same components throughout the drawings.

[0035] In the attached picture:

[0036] Figure 1 It is a flow chart of a direct-conversion gasification process energy-saving optimization method for adjusting the combustion air feed amount of a square box furnace provided by an embodiment of the present disclosure;

[0037] Figure 2 is a schematic diagram of a direct-conversion gasification process provided by another embodiment of the present disclosure;

[0038] Figure 3 is a trend diagram of flue gas residual oxygen content-air feed rate / fuel gas feed rate / combustion heat release under the current fuel gas feed rate of another embodiment of the present disclosure;

[0039] Figure 4 It is a trend chart of flue gas residual oxygen content-air feed amount / fuel gas change / by-product steam change / annual operating cost savings corresponding to the first strategy and the second strategy for energy-saving optimization provided in another embodiment of the present disclosure.

[0040] The present invention is further explained below in conjunction with the accompanying drawings and embodiments. DETAILED DESCRIPTION

[0041] The specific embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although the specific embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0042] It should be noted that certain words are used in the specification and claims to refer to specific components. Those skilled in the art should understand that technicians may use different nouns to refer to the same component. This specification and claims do not use the difference in nouns as a way to distinguish components, but use the difference in the functions of the components as the criterion for distinction. As mentioned throughout the specification and claims, "including" or "comprising" is an open term, so it should be interpreted as "including but not limited to". The subsequent description of the specification is a preferred embodiment of the present invention, but the description is based on the general principles of the specification and is not intended to limit the scope of the present invention. The scope of protection of the present invention shall be determined by the attached claims.

[0043] To facilitate understanding of the embodiments of the present invention, further explanation will be given below by taking specific embodiments as examples in conjunction with the accompanying drawings, and each of the accompanying drawings does not constitute a limitation on the embodiments of the present invention.

[0044] like Figures 1 to 4 As shown, the present invention discloses a direct-conversion gasification process optimization method for adjusting the combustion air feed amount of a square box furnace, comprising:

[0045] S100: Obtain the direct-to-gasification process flow, extract the current combustion data of the square box furnace, conduct a current baseline status assessment of the direct-to-gasification process, and build an Aspen Plus simulation model; building an Aspen Plus simulation model includes:

[0046] Process component input and physical property method selection;

[0047] The process building interface builds an industrial process, focusing on reflecting the key equipment and the corresponding stream input and output, connecting different equipment through streams to form a complete production process. In this method, the key equipment is the box furnace, process gas preheater and boiler feed water preheater, and the key streams are feed combustion air, fuel natural gas, combustion flue gas, raw gas, conversion gas, process gas and boiler feed water, such as Figure 2 shown.

[0048] Obtain and input the temperature, pressure, flow rate and composition of the above key streams, run to realize process simulation, and then read the thermal data of key equipment / streams.

[0049] S200: Based on the current fuel gas feed, the air feed rate of the square box furnace is adjusted in the Aspen Plus simulation model to construct the flue gas residual oxygen content and air feed rate (F air ), fuel gas feed rate (F fuel ) and combustion heat (Q total ) trend chart; by adjusting the combustion air feed rate of the square box furnace in the Aspen Plus simulation model, the flue gas residual oxygen content and combustion heat release data under different combustion air feed rates are read, and then the flue gas residual oxygen content and air feed rate (F air ), fuel gas feed rate (F fuel ) and combustion heat (Q total ) trend chart is constructed. With the help of Aspen Plus simulation, the calculation complexity is simplified, and the relationship between flue gas residual oxygen content-air feed amount-fuel gas feed amount-combustion heat release is directly obtained through simulation. Furthermore, this relationship can also be obtained by performing heat and mass balance on the combustion furnace, and further, the accuracy of the relationship can be improved through comparative correction.

[0050] S300: Based on the trend graph, obtain the current fuel gas feed rate and the current square box furnace heat demand and the air feed rate under the process gas preheater heat load and the boiler feed water preheater heat load with the flue gas residual oxygen content change trend, and record it as the first strategy; extract the thermal enthalpy of the by-product steam of the direct conversion process, and based on the boiler feed water preheater heat load change trend with the flue gas residual oxygen content, obtain the change of the by-product steam of the direct conversion gasification process under different flue gas residual oxygen contents; obtain the unit price of the by-product steam, and calculate the annual operating cost savings brought by the change of the by-product steam along with the flue gas residual oxygen content change trend;

[0051] S400, obtaining the combustion calorific value of the fuel natural gas, obtaining the current boiler feed water preheater heat load and the current square box furnace heat demand and the air feed amount and the fuel gas feed change amount under the process gas preheater heat load with the flue gas residual oxygen content change trend based on the trend chart, and recording it as the second strategy; obtaining the fuel gas unit price, calculating the annual operating cost savings brought by saving fuel gas with the flue gas residual oxygen content change trend;

[0052] S500: Draw a trend chart of flue gas residual oxygen content, air feed rate, fuel gas change, by-product steam change, and annual operating cost savings corresponding to the first strategy and the second strategy, and determine the economically optimal strategy under different flue gas residual oxygen content targets and its corresponding air feed rate, fuel gas change, and by-product steam change.

[0053] In a preferred embodiment of the direct-conversion gasification process optimization method for adjusting the combustion air feed amount of a square box furnace, in step S100, in the direct-conversion gasification process, the natural gas and steam mixture are respectively sent to the square box first-stage furnace and the heat exchange converter, and the two first-stage conversion gases are merged and enter the second-stage furnace. The heat source of the square box furnace is the combustion fuel gas, and the heat source of the heat exchange converter is the high-temperature second-stage conversion gas; the fuel gas is sent to the convection section coil of the first-stage converter and heated, and then used as fuel for the top burner and auxiliary burner of the square box converter. The flue gas from the first-stage converter enters the convection section to preheat the raw gas, fuel gas and air process gas and preheat the boiler feed water to produce by-product steam, and finally goes to the induced draft fan for discharge at the designed flue gas exhaust temperature.

[0054] In a preferred embodiment of the direct-conversion gasification process optimization method for adjusting the combustion air feed amount of a square box furnace, in step S100, the extracted current combustion data of the square box furnace includes the fuel gas feed amount, the air feed amount, the combustion heat release and the residual oxygen content in the flue gas; the current baseline state assessment of the direct-conversion gasification process includes assessing the heat requirement for the first stage conversion, the heat load of each process gas preheater, the heat load of the boiler feed water preheater and the designed flue gas temperature.

[0055] In a preferred implementation of the direct-conversion gasification process optimization method for adjusting the combustion air feed amount of a square box furnace, in step S200, the current fuel gas feed is maintained unchanged, and the combustion air feed amount of the square box furnace is gradually adjusted to obtain the changing trends of the flue gas residual oxygen content and the total combustion heat release under different fuel air feed amounts.

[0056] In the preferred embodiment of the direct conversion gasification process optimization method for adjusting the air feed amount of the square box furnace combustion, in step S300, in the first strategy, the air feed amount under different flue gas residual oxygen content is expressed as: F air，策略1 =F air , where F air，第一策略 represents the air feed rate in the first strategy, and the heat load of the boiler feed water preheater under different flue gas residual oxygen contents is expressed as:

[0057]

[0058] Where Q3 represents the heat load of the boiler feed water preheater; Qtota l represents the total heat released by combustion; Q1 represents the heat required for the first stage of conversion; Q2 represents the heat load of the process gas preheater; the superscript ini represents the current value; the change in the by-product steam under different flue gas residual oxygen content is expressed as:

[0059]

[0060] Where, ΔF steam Indicates the change in by-product steam; h steamrepresents the steam enthalpy; the annual operating cost savings under different flue gas residual oxygen content are expressed as:

[0061] ΔCo1=ΔF steam ·c steam

[0062] Where ΔCo1 represents the annual operating cost savings of the first strategy; c steam Indicates the unit price of steam.

[0063] In a preferred embodiment of the direct-conversion gasification process optimization method for adjusting the combustion air feed amount of a square box furnace, in step S400, in the second strategy, the air feed amount under different flue gas residual oxygen contents is expressed as:

[0064]

[0065] Among them, F air，第二策略 is the air feed amount in the second strategy.

[0066] In a preferred embodiment of the direct conversion gasification process optimization method for adjusting the combustion air feed amount of the square box furnace, in step S400, in the second strategy, the change in fuel gas feed under different flue gas residual oxygen content is expressed as:

[0067]

[0068] Where, ΔF fuel Indicates the change in fuel gas; q fuel Indicates the calorific value of fuel gas combustion.

[0069] In a preferred embodiment of the direct conversion gasification process optimization method for adjusting the combustion air feed amount of the square box furnace, in step S400, in the second strategy, the annual operating cost savings under different flue gas residual oxygen contents are expressed as:

[0070] ΔCo2=ΔF fuel ·c fuel , where ΔCo2 represents the annual operating cost savings of the second strategy; c fuel Indicates the unit price of natural gas fuel.

[0071] In a preferred implementation of the direct-conversion gasification process optimization method for adjusting the air feed amount of the square box furnace combustion, in step S500, the flue gas residual oxygen content is used as the horizontal axis, and the air feed amount, fuel gas change, by-product steam change and annual operating cost savings are used as the vertical axis to draw trend graphs of the flue gas residual oxygen content, air feed amount, fuel gas change, by-product steam change and annual operating cost savings corresponding to the first strategy and the second strategy respectively.

[0072] In a preferred embodiment of the direct-conversion gasification process optimization method for adjusting the air feed amount of the square box furnace combustion, for a given target residual oxygen content, the annual operating cost savings corresponding to the first strategy and the second strategy are determined respectively based on the flue gas residual oxygen content, air feed amount, fuel gas change, by-product steam change, and annual operating cost savings change trend chart: if ΔCo1>ΔCo2, the first strategy is an economically superior energy-saving scheme, the fuel gas consumption remains unchanged, the by-product steam consumption changes, and the air feed amount and by-product steam change at the target residual oxygen content are obtained from the trend chart; if ΔCo1<ΔCo2, the second strategy is an economically superior energy-saving scheme, the by-product steam consumption remains unchanged, the fuel gas consumption changes, and the air feed amount and fuel gas change at the target residual oxygen content are obtained from the trend chart.

[0073] In one embodiment, Figure 1 As shown, a method for energy-saving optimization of a direct-conversion gasification process for adjusting the combustion air feed amount of a square box furnace comprises the following steps:

[0074] S100: Obtain key equipment of the direct-transfer gasification process including box furnace, process gas preheater, boiler feed water preheater, and key process flows of the direct-transfer gasification process including combustion air, fuel natural gas, combustion flue gas, process gas, and boiler feed water; extract parameters such as heat load of key equipment, inlet and outlet temperature, flow rate and composition of key process flows, total heat release of fuel gas combustion, residual oxygen content of flue gas, and exhaust temperature;

[0075] In this step, key equipment such as the box furnace, process gas preheater, boiler feed water preheater, etc. are interconnected through key process flows such as combustion air, fuel natural gas, combustion flue gas, process gas, boiler feed water, etc. Figure 2 An exemplary display was performed.

[0076] Under the set exhaust gas temperature, the relationship between the total heat release of fuel gas combustion, the heat required for the first stage conversion, the heat load of the process gas preheater and the heat load of the boiler feed water preheater can be expressed as:

[0077] Q total =Q1+Q2+Q3 (1)

[0078] Among them, Q total It represents the total heat released by combustion; Q1 represents the heat required for the first stage of conversion; Q2 represents the heat load of the process gas preheater; Q3 represents the heat load of the boiler feed water preheater.

[0079] Based on the acquired parameters such as heat load of key equipment, inlet and outlet temperature, flow rate and composition of key process flow, total heat release of fuel gas combustion, residual oxygen content of flue gas and exhaust temperature, the Peng-Robinson physical property method was used to construct the Aspen Plus simulation model.

[0080] S200: Based on the current fuel gas feed rate, construct the flue gas residual oxygen content - air feed rate (F air ) / fuel gas feed amount (F fuel ) / Combustion heat release diagram (Q total );

[0081] In this step, the current fuel gas feed rate is maintained unchanged, and the combustion air feed rate is gradually adjusted to obtain the residual oxygen content of the flue gas at the outlet and the total heat release of combustion under different combustion air feed rates, and to construct a flue gas residual oxygen content-air feed rate / fuel gas feed rate / combustion heat release diagram. Figure 3 An exemplary display was performed.

[0082] S300: Based on the flue gas residual oxygen content-air feed rate / fuel gas feed rate / combustion heat release diagram of S200, obtain the current fuel gas feed rate and the current square box furnace heat demand and process gas preheater heat load (recorded as the first strategy) under the air feed rate and boiler feed water preheater heat load with flue gas residual oxygen content change trend; extract the thermal enthalpy of the by-product steam of the direct conversion process, based on the boiler feed water preheater heat load change trend with flue gas residual oxygen content, obtain the change of by-product steam of the direct conversion gasification process under different flue gas residual oxygen content; obtain the unit price of by-product steam, and calculate the annual operating cost savings brought by the change of by-product steam with the trend of flue gas residual oxygen content;

[0083] In this step, the fuel gas feed rate remains unchanged, and the air feed rate changes with the flue gas residual oxygen content as shown in step S200. Figure 3 As shown, it can be expressed as:

[0084] F air，策略1 =F air (2)

[0085] Among them, F air，第一策略 is the air feed amount in the first strategy.

[0086] The heat demand of the existing square box furnace and the heat load of the process gas preheater remain unchanged. The heat load of the boiler water preheater under different flue gas residual oxygen contents in the first strategy can be expressed as:

[0087]

[0088] The superscript ini indicates the current value.

[0089] Obtain the thermal enthalpy h of steam in the direct gasification process steam , then the change in by-product steam under different flue gas residual oxygen content in the first strategy can be expressed as:

[0090]

[0091] Where, ΔF steam Indicates the change in by-product steam.

[0092] Get the unit price c of steam in the direct gasification process steam , then the annual operating cost savings under different flue gas residual oxygen contents in the first strategy can be expressed as:

[0093] ΔCo1=ΔF steam ·c steam (5)

[0094] Wherein, ΔCo1 represents the annual operating cost savings of the first strategy.

[0095] S400, extract the combustion calorific value of natural gas fuel, based on the flue gas residual oxygen content-air feed amount / fuel gas feed amount / combustion heat release diagram of S200, obtain the change trend of air feed amount and fuel gas feed amount with flue gas residual oxygen content under the current boiler feed water preheater heat load and the current square box furnace heat demand and process gas preheater heat load (recorded as the second strategy); obtain the unit price of fuel gas, calculate the annual operating cost savings brought by saving fuel gas with the change trend of flue gas residual oxygen content;

[0096] In this step, the current boiler feed water preheater heat load, the current square box furnace heat demand and the process gas preheater heat load remain unchanged, that is, the total heat demand of the system remains unchanged, which can be expressed as:

[0097]

[0098] Under the current total heat demand of the system, the combustion air feed rate under different flue gas residual oxygen content in the second strategy can be expressed as:

[0099]

[0100] Among them, F air,第二策略 is the air feed amount in the second strategy;

[0101] Get the fuel gas combustion calorific value q fuel , then the change in fuel gas feed under different flue gas residual oxygen content in the second strategy can be expressed as:

[0102]

[0103] Where, ΔF fuel Indicates the change in fuel gas.

[0104] Obtain the unit price c of natural gas fuel in the direct gasification process fuel , then the annual operating cost savings under different flue gas residual oxygen contents in the second strategy can be expressed as:

[0105] ΔCo2=ΔF fuel ·c fuel (9)

[0106] Wherein, ΔCo2 represents the annual operating cost savings of the second strategy.

[0107] S500: Draw a trend chart of flue gas residual oxygen content - air feed rate / fuel gas change / by-product steam change / annual operating cost savings corresponding to the first strategy and the second strategy, and determine the most economically optimal energy-saving optimization strategy under different flue gas residual oxygen content targets and its corresponding air feed rate, fuel gas change and by-product steam change.

[0108] In this step, with the flue gas residual oxygen content as the horizontal axis, the air feed amount, the fuel gas change amount, the by-product steam change amount and the annual operating cost savings as the vertical axis, the flue gas residual oxygen content-air feed amount / fuel gas change amount / by-product steam change amount / annual operating cost savings corresponding to the first strategy and the second strategy are respectively drawn. Figure 4 shown.

[0109] The figure shows the difference between the current flue gas residual oxygen content and the target residual oxygen content. The flue gas residual oxygen content-annual operating cost savings curve shows the highest annual operating cost savings potential of the direct gasification system under different residual oxygen contents and its corresponding energy-saving optimization strategy. Combining the flue gas residual oxygen content-combustion air feed rate, flue gas residual oxygen content-fuel gas change, and flue gas residual oxygen content-byproduct steam change curves, the combustion air feed rate and the corresponding fuel gas feed change / byproduct steam change required to achieve the target residual oxygen content in the energy-saving optimization strategy can be obtained.

[0110] Next, a direct-conversion gasification process is optimized by using the existing method and the scheme disclosed in the present invention to further illustrate the technical effect of the scheme.

[0111] The optimal level of flue gas residual oxygen in existing direct gasification processes is usually determined by referring to industry standards and considering combustion efficiency and actual operating experience. The ideal value of flue gas residual oxygen in natural gas square box furnaces is 3-5%. In actual production, due to inappropriate feed rate, the flue gas residual oxygen content may be higher than the ideal value. In the design stage, process gas preheaters and boiler feed water preheaters are usually used to recover high-temperature flue gas waste heat.

[0112] The scheme disclosed in this disclosure is used to optimize the combustion air feed rate and energy / resource utilization efficiency of the square box furnace of the direct gasification process. The calculation data of each step are as follows:

[0113] In step S100, key equipment of the direct gasification process including the box furnace, process gas preheater, boiler feed water preheater and key process flows of the direct gasification process including combustion air, fuel natural gas, combustion flue gas, process gas and boiler feed water are obtained; parameters such as heat load of key equipment, inlet and outlet temperature, flow rate and composition of key process flows, heat release of fuel gas combustion, residual oxygen content of flue gas and exhaust temperature are extracted. Some parameters are shown in Table 1.

[0114] Table 1 Some parameters of a direct gasification process

[0115]

[0116] In step S200, based on the current fuel gas feed rate, the combustion air feed rate is gradually adjusted to obtain the outlet flue gas residual oxygen content and the total combustion heat release under different combustion air feed rates, as shown in Table 2.

[0117] Table 2 The residual oxygen content of the flue gas at the outlet and the total heat release of combustion at the current fuel gas feed rate and different combustion air feed rates

[0118] <![CDATA[Combustion air feed rate F air / t / h]]> 20.99 19.17 17.89 17.42 16.97 16.55 16.14 15.75 <![CDATA[Fuel gas feed rate F fuel / Nm 3 / h]]> 1100 1100 1100 1100 1100 1100 1100 1100 Residual oxygen content in flue gas / % 7.2 6 5 4.6 4.2 3.8 3.4 3 <![CDATA[Total heat release of combustion Q total / kW]]> 10091 10149 10190 10205 10220 10234 10247 10259

[0119] In step S300, the current fuel gas feed rate and the current square box furnace heat requirement and the air feed rate under the process gas preheater heat load, the fuel gas feed change, the boiler feed water preheater heat load, the by-product 1.45MPa steam change and the annual operating cost savings brought by the by-product steam change are obtained as the flue gas residual oxygen content changes as shown in Table 3.

[0120] Table 3 Air feed rate, boiler feed water preheater heat load, by-product steam change and annual operating cost savings for different flue gas residual oxygen contents in the first strategy

[0121] Residual oxygen content in flue gas / % 7.2 6 5 4.6 4.2 3.8 3.4 3 Combustion air feed rate / t / h 20.99 19.17 17.89 17.42 16.97 16.55 16.14 15.75 <![CDATA[Fuel gas feed change amount / Nm 3 / h]]> 0 0 0 0 0 0 0 0 Boiler feed water preheater heat load / kW 861 920 961 976 990 1004 1017 1030 Byproduct steam change / t / h 0.00 0.11 0.18 0.21 0.24 0.26 0.29 0.31 Annual operating cost savings / 10,000 yuan / year 0.00 14.65 24.97 28.76 32.38 35.83 39.12 42.27

[0122] In step S400, the current boiler feed water preheater heat load, the current square box furnace heat requirement and the process gas preheater heat load are obtained, and the air feed rate, the fuel gas feed change, the by-product 1.45MPa steam change and the annual operating cost savings brought about by the fuel gas feed change are changed with the flue gas residual oxygen content as shown in Table 4.

[0123] Table 4 The corresponding air feed rate, fuel gas feed rate change and annual operating cost savings for different flue gas residual oxygen contents in the second strategy

[0124] Residual oxygen content in flue gas / % 7.2 6 5 4.6 4.2 3.8 3.4 3 Combustion air feed rate / t / h 20.99 19.06 17.72 17.23 16.76 16.31 15.89 15.49 <![CDATA[Fuel gas feed change amount / Nm 3 / h]]> 0.00 6.28 10.70 12.33 13.88 15.36 16.77 18.12 Byproduct steam change / t / h 0 0 0 0 0 0 0 0 Annual operating cost savings / 10,000 yuan / year 0.00 15.07 25.68 29.59 33.31 36.86 40.24 43.48

[0125] In step S400, Table 3 and Table 4 are combined to draw a trend graph of flue gas residual oxygen content-air feed amount / fuel gas change amount / by-product steam change amount / annual operating cost savings corresponding to the first strategy and the second strategy.

[0126] From Table 1, we can see that the current flue gas residual oxygen content is 7.2%, which is higher than the ideal value. If the flue gas residual oxygen content is reduced to 5%, the maximum annual operating cost savings can reach 256,800 yuan / year. The corresponding energy-saving optimization plan is the second strategy. At this time, the by-product steam volume should be maintained unchanged. From Table 4, we can see that the fuel gas consumption can be reduced by 10.70Nm 3 / h; the combustion air feed rate should be adjusted from the current value of 20.99t / h to 17.72t / h.

[0127] It can be concluded that the combustion air feed rate of the direct-conversion gasification process is optimized by using the scheme disclosed in the present invention, and the optimal energy-saving optimization strategy of the system is determined, with the goal of reducing the residual oxygen content in the flue gas to 5%. After optimization, the combustion air feed rate is 17.72 t / h, and the corresponding energy-saving optimization strategy is the second strategy - the amount of by-product steam remains unchanged, and the amount of fuel gas used changes, which can save 256,800 yuan in annual operating costs.

[0128] At present, the residual oxygen content of flue gas in the direct gasification process is 7.2%. According to Table 1, the fuel air feed rate is 20.99t / h and the fuel gas feed rate is 1100Nm 3 / h. Therefore. By optimizing the combustion air feed rate of the direct gasification process using the scheme disclosed in the present invention, the air feed rate per unit time can be reduced by about 15.59%, the fuel gas feed rate per unit time can be saved by 0.97%, and the annual operating cost can be saved by 256,800 yuan.

[0129] In the current direct-conversion gasification combustion system, the residual oxygen content in the flue gas is often higher than the ideal level (3-5%), and there is a situation where the combustion air feed amount is excessive. This inappropriate feed will reduce the thermal efficiency of combustion and cause unnecessary waste of energy or resources. The energy-saving optimization method and optimization strategy of the direct-conversion gasification process for adjusting the combustion air feed amount of the square box furnace described in the present invention are based on the extraction of current production data and strict simulation calculations, clarify the correlation between the residual oxygen content in the flue gas and the air feed amount, and use increasing by-product steam and saving fuel gas as energy-saving optimization strategies respectively. The annual operating cost saving potential of the system under different flue gas residual oxygen content targets is explored, and the maximum annual operating cost saving is used as an economic evaluation indicator to determine the optimal energy-saving optimization strategy. The energy-saving optimization scheme, theoretical value of air feed amount and annual operating cost saving obtained are accurate and effective, which are of great significance for guiding industrial parameter adjustment and energy-saving optimization.

[0130] In one embodiment, the direct-conversion gasification process is obtained, the current combustion data of the square box furnace is extracted, the current baseline state of the direct-conversion gasification process is evaluated, and an Aspen Plus simulation model is constructed; based on the current fuel gas feed, a flue gas residual oxygen content-air feed amount / fuel gas feed amount / combustion heat release diagram is constructed; based on the diagram and the steam enthalpy, the air feed amount and the change in by-product steam corresponding to different flue gas residual oxygen contents in the first strategy are obtained, and based on the steam unit price, the annual operating cost savings are obtained; based on the diagram and the fuel gas combustion calorific value, the air feed amount and the change in fuel gas feed corresponding to different flue gas residual oxygen contents in the second strategy are obtained, and based on the fuel gas unit price, the annual operating cost savings are obtained; a flue gas residual oxygen content-air feed amount / fuel gas change / by-product steam change / annual operating cost savings change trend diagram corresponding to the first strategy and the second strategy is drawn to determine the most economically optimal energy-saving optimization strategy under different flue gas residual oxygen targets and its corresponding air feed amount, fuel gas change and by-product steam change.

[0131] Although the embodiments of the present invention are described above in conjunction with the accompanying drawings, the present invention is not limited to the above specific embodiments and application fields, and the above specific embodiments are only illustrative and instructive, rather than restrictive. A person of ordinary skill in the art can also make many forms under the guidance of this specification and without departing from the scope of protection of the claims of the present invention, all of which belong to the protection of the present invention.

Claims

1. A method for optimizing a direct-conversion gasification process for adjusting the amount of combustion air feed in a square box furnace, characterized in that: include: S100: Obtain the direct-to-gasification process flow, extract the current combustion data of the square box furnace, conduct a current baseline status assessment of the direct-to-gasification process, and build an Aspen Plus simulation model; S2 00: Based on the current fuel gas feed, adjust the air feed rate of the square box furnace in the Aspen Plus simulation model to build the flue gas residual oxygen content and air feed rate (F air ), fuel gas feed rate (F fuel ) and combustion heat (Q total ) trend chart; S300: based on the trend graph, obtain the current fuel gas feed rate and the current square box furnace heat demand and the air feed rate under the process gas preheater heat load and the boiler feed water preheater heat load with flue gas residual oxygen content change trend, and record it as the first strategy; Extract the thermal enthalpy of the by-product steam of the direct conversion process, and obtain the change of the by-product steam of the direct conversion gasification process under different flue gas residual oxygen contents based on the variation trend of the heat load of the boiler feed water preheater; Obtain the unit price of by-product steam and calculate the annual operating cost savings brought about by the change of by-product steam along with the change trend of flue gas residual oxygen content; S400, obtaining the combustion calorific value of the fuel natural gas, obtaining the current boiler feed water preheater heat load and the current square box furnace heat demand and the air feed amount and the fuel gas feed change amount under the process gas preheater heat load with the flue gas residual oxygen content change trend based on the trend chart, and recording it as the second strategy; obtaining the fuel gas unit price, calculating the annual operating cost savings brought by saving fuel gas with the flue gas residual oxygen content change trend; S500: Draw a trend chart of flue gas residual oxygen content, air feed rate, fuel gas change, by-product steam change, and annual operating cost savings corresponding to the first strategy and the second strategy, and determine the economically optimal strategy under different flue gas residual oxygen content targets and its corresponding air feed rate, fuel gas change, and by-product steam change.

2. The method for optimizing the direct-conversion gasification process for adjusting the combustion air feed amount of a square box furnace according to claim 1, characterized in that: Preferably, in step S100, in the direct conversion gasification process, the natural gas and steam mixture are respectively sent to the square box first stage furnace and the heat exchange reformer, and the two first stage reformed gases are merged and enter the second stage furnace. The heat source of the square box furnace is the combustion fuel gas, and the heat source of the heat exchange reformer is the high-temperature second stage reformed gas; the fuel gas is sent to the convection section coil of the first stage reformer for heating and then used as fuel for the top burner and auxiliary burner of the square box reformer, and the flue gas from the first stage reformer enters the convection section to preheat the raw gas, fuel gas and air process gas and preheat the boiler feed water to produce by-product steam, and finally goes to the induced draft fan for discharge at the designed flue gas exhaust temperature.

3. The method for optimizing the direct-conversion gasification process for adjusting the combustion air feed amount of a square box furnace according to claim 1, characterized in that: In step S100, the current combustion data of the square box furnace is extracted, including the fuel gas feed rate, the air feed rate, the combustion heat release and the flue gas residual oxygen content; the current benchmark state assessment of the direct conversion gasification process includes assessing the heat requirement of the first stage conversion, the heat load of each process gas preheater, the heat load of the boiler feed water preheater and the designed flue gas temperature.

4. The method for optimizing the direct-conversion gasification process for adjusting the combustion air feed amount of a square box furnace according to claim 1 is characterized in that: In step S200, the current fuel gas feed is maintained unchanged, and the combustion air feed rate of the square box furnace is gradually adjusted to obtain the flue gas residual oxygen content and the total combustion heat release change trend under different fuel air feed rates.

5. The method for optimizing the direct-conversion gasification process for adjusting the combustion air feed amount of a square box furnace according to claim 1, characterized in that: In step S300, in the first strategy, the air feed rate under different flue gas residual oxygen content is expressed as: F air，策略1 =F air , where F air，第一策略 represents the air feed rate in the first strategy, and the heat load of the boiler feed water preheater under different flue gas residual oxygen contents is expressed as: Among them, Q3 represents the heat load of boiler feed water preheater; Q total represents the total heat released by combustion; Q1 represents the heat required for the first stage of conversion; Q2 represents the heat load of the process gas preheater; the superscript ini represents the current value; the change in the by-product steam under different flue gas residual oxygen content is expressed as: Where, ΔF steam Indicates the change in by-product steam; h steam represents the steam enthalpy; the annual operating cost savings under different flue gas residual oxygen content are expressed as: ΔCo1=ΔF steam ·c steam , Where ΔCo1 represents the annual operating cost savings of the first strategy; c steam Indicates the unit price of steam.

6. The method for optimizing the direct-conversion gasification process for adjusting the combustion air feed amount of a square box furnace according to claim 1, characterized in that: In step S400, in the second strategy, the air feed amount under different flue gas residual oxygen contents is expressed as: Among them, F air，第二策略 is the air feed amount in the second strategy.

7. The method for optimizing the direct-conversion gasification process for adjusting the combustion air feed amount of a square box furnace according to claim 1, characterized in that: In step S400, in the second strategy, the change in fuel gas feed under different flue gas residual oxygen contents is expressed as: Where, ΔF fuel Indicates the change in fuel gas; q fuel Indicates the calorific value of fuel gas combustion.

8. The method for optimizing the direct-conversion gasification process for adjusting the combustion air feed amount of a square box furnace according to claim 1, characterized in that: In step S400, in the second strategy, the annual operating cost savings under different flue gas residual oxygen contents are expressed as: ΔCo2=ΔF fuel ·c fuel , where ΔCo2 represents the annual operating cost savings of the second strategy; c fuel Indicates the unit price of natural gas fuel.

9. The method for optimizing the direct-conversion gasification process for adjusting the combustion air feed amount of a square box furnace according to claim 1, characterized in that: In step S500, with the flue gas residual oxygen content as the horizontal axis and the air feed amount, fuel gas change, by-product steam change and annual operating cost savings as the vertical axis, the trend graphs of the flue gas residual oxygen content, air feed amount, fuel gas change, by-product steam change and annual operating cost savings corresponding to the first strategy and the second strategy are drawn respectively.

10. A direct-conversion gasification process optimization method for adjusting the combustion air feed amount of a square box furnace according to claim 9, characterized in that: For a given target residual oxygen content, the annual operating cost savings corresponding to the first strategy and the second strategy are determined respectively based on the trend chart of flue gas residual oxygen content, air feed rate, fuel gas change, by-product steam change, and annual operating cost savings: if ΔCo1>ΔCo2, the first strategy is the more economical energy-saving scheme, the fuel gas consumption remains unchanged, the by-product steam consumption changes, and the air feed rate and by-product steam change at the target residual oxygen content are obtained from the trend chart; if ΔCo1<ΔCo2, the second strategy is the more economical energy-saving scheme, the by-product steam consumption remains unchanged, the fuel gas consumption changes, and the air feed rate and fuel gas change at the target residual oxygen content are obtained from the trend chart.

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