Measurement method of combustion space data for underground coal gasification

Abstract

The invention relates to the technical field of methods for measuring the volume and residence time distribution of a combustion space area, in particular to a method for measuring the data of the combustion space area for underground coal gasification, which is used for industrial underground coal gasification projects. According to the method, the volume and the retention time distribution of the combustion space area in the production process of the coal underground gasification project and after production halt are measured and calculated according to the concentration, the time change and the total amount in different gasification modes, existing production and monitoring equipment of an industrial project coal underground gasification furnace production system is adopted, and expensive raw materials and equipment do not need to be additionally added; the measurement method does not influence the normal production process of underground coal gasification and downstream products thereof, the influence of background values and errors of instruments and equipment on data is extremely low, the obtained result is more accurate, and technical improvement is facilitated.

Description

Technical Field

[0001] The invention relates to the technical field of methods for measuring the volume and residence time distribution of a combustion void zone, and in particular to a method for measuring combustion void zone data for underground coal gasification. Background Art

[0002] Underground coal gasification (ISC) is a process that converts coal directly into product gas, usually called synthesis gas, by combustion and gasification of underground coal seams in the presence of an oxidant. The synthesis gas can then be used as a feedstock for a variety of applications, including fuel production, chemical production, and power generation. This underground coal gasification technology is applicable to most coal deposits. In view of the increasingly stringent environmental requirements for the mining industry and considering the related labor and infrastructure costs, this technology is undoubtedly very attractive.

[0003] Surface wells are drilled directly into the coal seam, providing an effective channel for oxidant injection and product gas production. A pair of wells are connected or extended horizontally underground to form a substantially horizontal drilling channel (also referred to as a coal seam well or connecting channel). This channel facilitates oxidant injection, growth of the combustion zone and product gas transportation. A well used for oxidant injection is called an "injection well" and the other well used for producing product gas is called a "product well". Both directional horizontal drilling and vertical drilling can be used as injection wells or product wells. Underground coal gasification (ISC) may also require the use of one or more vertical wells (e.g., functional wells and auxiliary wells) between the injection well and the product well.

[0004] When there are injection wells, product wells and horizontal channels connecting the two in a coal seam, this structure is called an underground coal gasification (ISC) unit or well pair. The ISC unit includes a combustion zone, a gasification zone and a pyrolysis zone. Among them, the combustion zone is near the oxidant injection point in the coal seam; the gasification zone surrounds the combustion zone in a radial form or is downstream of the combustion zone, and the coal is gasified and partially oxidized in the gasification zone to generate product gas; the pyrolysis zone is downstream of the gasification zone, and the pyrolysis reaction of coal generally occurs here. The high-temperature product gas flows downstream from the gasification zone and is eventually transported to the ground from the wellhead of the product well. While the coal is burning or gasifying, the ISC combustion zone in the coal seam will grow and become larger.

[0005] The ISC gas gap in coal seams is a very important part of underground coal gasification research. The commonly used research method is to simulate the growth process of the gas gap by establishing a finite element model. The shape and volume of the gas gap can be seen in the simulation software. However, in the actual operation of underground coal gasification, it is usually difficult to directly measure the shape and volume of the gas gap because it is deep underground, so it is impossible to examine the accuracy of the above model.

[0006] The existing methods for measuring the volume of the gas-filled zone mainly include: geophysical exploration technology, core drilling method, and radioactive isotope tracers. Geophysical exploration technologies include seismic wave method and resistivity tomography. The seismic wave method is relatively expensive, has limited resolution, and has large interpretation errors for deep coal seams and complex geological conditions; while resistivity tomography has limited resolution and depth penetration capabilities and is greatly affected by surface conditions. The core drilling method is costly, time-consuming, and destructive. It can only reflect the situation on the borehole path and is difficult to fully evaluate the entire gas-filled zone; radioactive isotope tracers are expensive, have a large range of equipment measurement errors, and involve issues of safe management and handling of radioactive materials. The scope of application is limited and it is not applicable to all areas.

[0007] For example, CN102567649A discloses a volume modeling method for underground coal seam gas voids. Starting from the basic theory of heat conduction, based on the high temperature of the gas voids and the relative constant temperature of the conventional underground temperature field, the temperature field control equation under the action of the gas voids is derived by analyzing the influence mechanism of the seepage on the temperature field; the Bessel function is introduced to derive the temperature field distribution equation around the combustion channel, and the finite element numerical solution is given. With the help of on-site temperature detection data, the temperature field distribution under the action of the gas voids is inverted using the finite element numerical software, and the high temperature influence boundary of the combustion channel is determined; by adjusting the cross-sectional size of the gas voids, the coal seam temperature distribution with the best fit to the on-site detection is obtained, and the shape and size of the underground coal combustion gas voids are inverted, and then the approximate volume of the gas voids is calculated. The calculation process of the above method is too complicated and too theoretical, and its practicality is poor in actual engineering applications.

[0008] For example, CN102607663A discloses a method and device for detecting the volume of an underground cavity. The specific method is to fill the underground cavity with water or the underground cavity is already filled with water, add a known amount of detectable reagent of A0mg to the underground cavity; after the detectable reagent is evenly distributed in the water, the concentration of the detectable reagent in the water is detected C'mg / L; according to V=V'=A0 / C' / 1000m3. Since it is necessary to fill the cavity with water, detection cannot be carried out when the normal production process is running. Usually, such detection can only be carried out in the late operation of the gasifier, because the detection requires a large amount of water to be filled into the gasifier, which will affect the further ignition, combustion and gasification of the gasifier. Due to the introduction of fresh water, some water with detection reagents may enter the stratum from the combustion zone along the direction of the movement of the groundwater and enter the cracks caused by sedimentation after the gasification is completed, so this method has inaccuracy. In addition, where coalbed methane is available, coalbed methane will accumulate at high points and replace water, which also affects the accuracy. In the late stage of gasifier operation, the volume of the combustion zone will be very large. According to the typical data of the late stage of normal combustion zone, the combustion zone is about 1,400 meters long, about 20 meters wide, and the coal seam is about 10 meters thick, so the volume reaches an astonishing 280,000 cubic meters. The amount of water and detectable reagents required for monitoring are too large, and drainage after detection is also a big problem. Therefore, for the normal operation of industrial underground coal gasification equipment, this detection method is not very practical.

[0009] For example, CN107630694A discloses a method for obtaining the volume of the underground coal gasification gasification zone. The underground gasification furnace is simulated by a ground gasification furnace to obtain the volume of the gasification gasification zone. The calculation involves the carbon content of the coal and the content of CH4, CO and CO2 in the synthesis gas. The volume of the underground coal gasification gasification zone is calculated by carbon balance, which seems to be more accurate. Among them, the critical ground gasification furnace simulation, from the perspective of the current technical development level, is basically impossible to achieve accurate simulation of underground gasification conditions, especially for the high-pressure, pure oxygen gasification process of deep coal seams. First, there is a significant error in the functional relationship between the carbon balance in the ground simulation test and the actual volume of the underground gasification zone, and the final calculation does not obtain the accurate volume of the gasification zone. Secondly, from the perspective of the long-term operation of underground coal gasification, the carbon content in the coal at different parts of the gasification furnace may vary greatly, and if there is coalbed methane, it will contain more CH4 gas, which seriously affects the carbon balance. If these errors are large, the error in calculating the volume of the gasification zone will also become large.

[0010] In order to solve the above problems, a method for measuring combustion air zone data for underground coal gasification is proposed in this application. Summary of the invention

[0011] The present invention provides a method for measuring the volume and residence time distribution of a combustion void zone in an underground coal gasification industrialization project, so as to reduce the influence of the error of the measuring equipment on the accuracy of the result.

[0012] The present invention mainly provides a method for measuring the combustion zone data of underground coal gasification, by adjusting the nitrogen content in the underground gasification furnace, and obtaining the combustion zone data based on the adjusted nitrogen content.

[0013] A further technical solution is defined as follows: the fuel-gap zone data is fuel-gap zone volume data.

[0014] A further technical solution is defined as follows: adjusting the nitrogen content of the underground gasifier is to reduce the nitrogen content of the underground gasifier.

[0015] A further technical solution is defined as follows: when the air gasification mode reaches a stable state, the synthesis gas flow rate is set to V1, and the nitrogen content of the synthesis gas is set to C1; a gasifying agent with a preset oxygen content is obtained and injected into the combustion and air zone, and the time at this time is recorded as t0;

[0016] Obtain the gasifying agent flow rate, and divide the length L1 of the injection well gasifying agent pipeline by the gasifying agent flow rate to obtain the gasifying agent injection lag time Δt1. Assuming that the time for the gasifying agent to reach the combustion zone through the injection well gasifying agent pipeline is t'0, then t'0 = t0 + Δt1;

[0017] Obtain the syngas flow rate, and divide the length L2 from the outlet of the combustion zone to the gas flow meter of the syngas pipeline by the syngas flow rate to obtain the lag time Δt2 of the syngas. Then, the time from t'0 to t1 after Δt2 of the syngas passing through the syngas pipeline of the product well to reach the gas flow meter is t1, so t1=t'0+Δt2;

[0018] The gas flow meter measures and records the synthesis gas flow rate in real time from time t1 until the nitrogen content of the synthesis gas remains basically unchanged. At this time, the time is t n , let t n The synthesis gas flow rate at the moment is V n The nitrogen content of the synthesis gas is C n , the timing period is t1~t n ;

[0019] Calculate the total nitrogen content in the combustion zone.

[0020] Where: Q——Total nitrogen content in the combustion-air zone at the beginning of timing, Nm 3 ;

[0021] V(t)——The flow rate of synthesis gas during the timing period, Nm 3 / h;

[0022] C(t)——Nitrogen content of synthesis gas during the timing period;

[0023] V n ——The flow rate of synthesis gas when the nitrogen content of synthesis gas is stable at the end of the timing, Nm 3 / h;

[0024] C n ——The nitrogen content of the synthesis gas when the nitrogen content of the synthesis gas is stable at the end of the timing;

[0025] ξ——The proportion of nitrogen flow rate escaping from the underground gasifier, converted into ammonia and lost by adsorption to the total nitrogen, which is about 0.5%-3%;

[0026] t1——time when timing starts;

[0027] t n ——The time when the timing ends;

[0028] Obtain the partial pressure P of nitrogen in the combustion-air zone at the end of the timing N ; The partial pressure of nitrogen in the combustion-air zone at the end of the timing P N It is equal to the total pressure of the combustion zone P multiplied by the nitrogen content C of the synthesis gas at this time n ,Right now:

[0029] P N =P×C n ;

[0030] Based on P N Get the molar volume V of nitrogen m ; Then the volume of the combustion space is:

[0031]

[0032] Where V is the volume of the combustion space, m 3 ;

[0033] n——the amount of nitrogen, mol,

[0034] Q——Total nitrogen content in the combustion-air zone at the end of the timing, Nm 3 .

[0035] A further technical solution is defined as follows: adjusting the nitrogen content of the underground gasifier is to increase the nitrogen content of the underground gasifier.

[0036] A further technical solution is defined as follows: when the oxygen gasification mode reaches a stable state, the synthesis gas flow rate is set to V1, the nitrogen content of the synthesis gas is set to C1, the oxygen supply system reduces the oxygen supply to a preset flow rate, and the air compressor station system is turned on to inject air or nitrogen so that the oxygen content of the mixed gas as a gasifying agent reaches a preset percentage, and the time at this time is set to t0; if nitrogen is directly injected during the late shutdown stage of the gasifier, the time to start injecting nitrogen is t0;

[0037] Obtain the gasifying agent flow rate, and divide the length L1 of the injection well gasifying agent pipeline by the gasifying agent flow rate to obtain the gasifying agent injection lag time Δt1. Assuming that the time for the gasifying agent to reach the combustion zone through the injection well gasifying agent pipeline is t'0, then t'0 = t0 + Δt1;

[0038] Obtain the syngas flow rate, and divide the length L2 from the outlet of the combustion zone to the gas flow meter of the syngas pipeline by the syngas flow rate to obtain the lag time Δt2 of the syngas. Then, the time from t'0 to t1 after Δt2 of the syngas passing through the syngas pipeline of the product well to reach the gas flow meter is t1, so t1=t'0+Δt2;

[0039] The gas flow meter measures and records the synthesis gas flow rate in real time from time t1 until the nitrogen content of the synthesis gas remains basically unchanged. At this time, the time is t n , let t n The synthesis gas flow rate at the moment is V n The nitrogen content of the synthesis gas is C n , the timing period is t1~t n ;

[0040] Calculate the total nitrogen content in the combustion zone.

[0041]

[0042] Where: Q——Total nitrogen content in the combustion-air zone at the end of the timing, Nm 3 ;

[0043] V0——injection gas flow rate, Nm 3 / h;

[0044] C0——nitrogen content of injected gas;

[0045] V(t)——The flow rate of synthesis gas during the timing period, Nm 3 / h;

[0046] C(t)——Nitrogen content of synthesis gas during the timing period;

[0047] V1——synthetic gas flow rate at the start of timing, Nm 3 / h;

[0048] V n——The flow rate of synthesis gas at the end of the timing, Nm 3 / h;

[0049] C1——Nitrogen content of synthesis gas at the beginning of timing;

[0050] C n ——Nitrogen content of synthesis gas at the end of timing;

[0051] ΔT——total timing time, h;

[0052] ξ——Ratio of nitrogen flow rate escaping from underground gasifier, converted into ammonia and lost by adsorption to total nitrogen;

[0053] T1——time when timing starts;

[0054] t n ——The time when the timing ends;

[0055] Obtain the partial pressure P of nitrogen in the combustion-air zone at the end of the timing N ; The partial pressure of nitrogen in the combustion-air zone at the end of the timing P N It is equal to the total pressure of the combustion zone P multiplied by the nitrogen content C of the synthesis gas at this time n ,Right now:

[0056] P N =P×C n ;

[0057] Based on P N Get the molar volume V of nitrogen m ; Then the volume of the combustion space is:

[0058]

[0059] Where V is the volume of the combustion space, m 3 ;

[0060] n——the amount of nitrogen, mol,

[0061] Q——Total nitrogen content in the combustion-air zone at the end of the timing, Nm 3 .

[0062] 7. The method for measuring the combustion zone data of underground coal gasification according to claim 4 or 6, characterized in that: the molar volume V of nitrogen is m The calculation is performed using the Peng-Robinson gas state equation, specifically:

[0063]

[0064] Where: P N ——Nitrogen partial pressure in the combustion space, Pa;

[0065] R——ideal gas constant, R=8.314J / (mol·K);

[0066] T——absolute temperature of gas in combustion zone, K;

[0067] V m ——The molar volume of nitrogen under these conditions, m3 / mol;

[0068] b——Parameters related to the characteristics of nitrogen substances, Tc——Nitrogen critical temperature, Pc——Nitrogen critical pressure;

[0069]

[0070] c(T)——is a temperature-dependent correction factor,

[0071] Where k = 0.37464 + 1.54226ω - 0.26992ω 2 ;

[0072] Where ω is the eccentricity factor of nitrogen.

[0073] A further technical solution is defined as follows: when the oxygen gasification mode reaches a stable state, the oxygen supply system reduces the oxygen supply to a preset flow rate, and the air compression station system is turned on to inject air so that the oxygen content of the mixed gas as a gasifying agent reaches a preset value, and the time at this time is set as t0;

[0074] The gas flow rate of the injected gasifier is V0, the nitrogen content of the injected gas is C0, before the injection of air and nitrogen, when the oxygen gasification mode reaches a stable state, the synthesis gas flow rate is V1, the nitrogen content of the synthesis gas is C1, then the nitrogen at this time comes from the nitrogen generated by the nitrogen element in the coal and the nitrogen protection of the underground gasifier, which is V1C1. The mixed gas of air and oxygen is injected at time t0;

[0075] Obtain the gasifying agent flow rate, and divide the length L1 of the injection well gasifying agent pipeline by the gasifying agent flow rate to obtain the gasifying agent injection lag time Δt1. Assuming that the time for the gasifying agent to reach the combustion zone through the injection well gasifying agent pipeline is t'0, then t'0 = t0 + Δt1;

[0076] Obtain the syngas flow rate, and divide the length L2 from the outlet of the combustion zone to the gas flow meter of the syngas pipeline by the syngas flow rate to obtain the lag time Δt2 of the syngas. Then, after Δt2 time from time t'0, the time when the syngas passes through the syngas pipeline of the product well and reaches the gas flow meter is t1, and t1=t'0+Δt2. Then, the syngas flow rate and the syngas nitrogen content are measured from time t1;

[0077] Assume that the nitrogen content of the outlet synthesis gas finally reaches the maximum value Ca and does not change any more. The time at this time is tn. The timing ends at this time. The timing measurement period is t1 to t n , assuming t1 = 0, the total time of the timing period T = t n -t1. Assume that the volume of the combustion zone is Q, and the time after t1 = 0 is t (0≤t≤ΔT), then the outlet synthesis gas flow is V(t), the nitrogen content is C(t), and the nitrogen concentration in the combustion zone is C'(t), so: C'(0) = C(0), C'(ΔT) = C a ;

[0078] At time t, according to the nitrogen balance of the system:

[0079]

[0080] Where: V0——injected gasifying agent flow rate, Nm 3 / h;

[0081] C0——nitrogen content of injected gasifying agent;

[0082] V1——synthetic gas flow rate at the start of timing, Nm 3 / h;

[0083] C1——Nitrogen content of synthesis gas at the beginning of timing;

[0084] t——the time when the injection of gasifying agent starts, h;

[0085] Q——combustion space volume, m 3 , can be calculated according to the second method of measuring the volume of the combustion void area; C'(t)——nitrogen concentration in the combustion void area at time t, Nm 3 / m 3 ;

[0086] V(t)——Export syngas flow rate at time t, Nm 3 / h;

[0087] C(t)——nitrogen content of outlet syngas at time t;

[0088] The cumulative distribution function based on the residence time is: Among them, ΔT is the total timing time;

[0089] When t = ΔT:

[0090]

[0091] Where: Ca——the maximum nitrogen content of the outlet synthesis gas;

[0092]

[0093] Where, F(t) – cumulative distribution function of residence time;

[0094] E(t)——residence time distribution function;

[0095] The cumulative distribution function of the residence time is:

[0096]

[0097] Average stay time:

[0098]

[0099] variance:

[0100]

[0101] For discrete data, we have:

[0102] Dwell time distribution function:

[0103] Cumulative distribution function of residence time:

[0104] Average stay time:

[0105] variance:

[0106] Beneficial effects of the present invention:

[0107] The present invention adopts the existing production and detection equipment of the underground coal gasification furnace production system of the industrial project to form a new measurement system, which does not require the addition of expensive raw materials and equipment and has good economic efficiency. The adopted method has an accurate measurement process, effectively reduces the influence of the error of the measurement equipment on the accuracy of the result, and the obtained result is more accurate, which is conducive to technical improvement. BRIEF DESCRIPTION OF THE DRAWINGS

[0108] Figure 1 Shown is a schematic diagram of the device system used in the method for measuring the combustion air zone data of underground coal gasification of the present invention. DETAILED DESCRIPTION

[0109] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0110] The present invention provides an embodiment: a method for measuring gas void zone data for underground coal gasification, the method comprising measuring the gas void zone volume and the gas void zone residence time distribution.

[0111] There are two methods for measuring the volume of the gas void area described in the present invention: measuring the volume of the gas void area by injecting oxygen to reduce the nitrogen content in the gasifier; measuring the volume of the gas void area by injecting air or nitrogen to increase the nitrogen content in the gasifier; after adjusting the nitrogen content, the volume of the gas void area is calculated by DCS process parameters, nitrogen material balance and chemical thermodynamics related knowledge. The volume of the gas void area can be used to guide the control of production process parameters and the parameter design of the later shutdown, well sealing and backfilling. In addition, the production conditions of the underground coal gasification process can be judged by mutual verification of the gas void area volume data and the coal consumption value of the process balance.

[0112] Furthermore, this embodiment first describes a method for reducing nitrogen content, specifically:

[0113] When the air gasification mode reaches a stable state, the syngas flow rate is V1 and the syngas nitrogen content is C1; at this time, the oxygen supply system is opened to the preset value to obtain a gasifier with an oxygen content of 30-35 mole% to be injected into the combustion zone, and the time at this time is recorded as t0; air and oxygen can be mixed on the ground into the air injection pipeline leading to the injection well. Within these oxidant composition ranges, the nitrogen content in the dry syngas will drop from about 45-50 mol% to 30-40 mol%. The nitrogen content is reduced by 10-15 mole%, and the measurement target value far exceeds the inherent error of the measuring instrument. For industrial projects with 10-200 gasifiers running at the same time, the change in the total syngas nitrogen content is only 0-2 mole%, which will not affect the normal production of the downstream process of air gasification;

[0114] The gasifier flow rate of 30-35 mol% oxygen is measured and calculated. The length L1 of the gasifier pipeline of the injection well is divided by the gasifier flow rate to obtain the gasifier injection lag time Δt1. Assuming that the time for the gasifier to reach the combustion zone through the gasifier pipeline of the injection well is t'0, then t'0 = t0 + Δt1;

[0115] Measure and calculate the synthesis gas flow rate at this time, and divide the length L2 from the outlet of the combustion zone to the gas flow meter of the synthesis gas pipeline by the synthesis gas flow rate to obtain the lag time Δt2 of the synthesis gas. Then, the time from t'0 to t1 after Δt2 of the synthesis gas passing through the product well synthesis gas pipeline to the gas flow meter is t1, so t1=t'0+Δt2;

[0116] Starting from time t1, the gas flowmeter measures and records the synthesis gas flow in real time, and the online gas analyzer measures and records the nitrogen content of the synthesis gas in real time, with an interval of 5-60 seconds. The manual gas chromatograph measures the composition of the synthesis gas every 20-30 minutes to calibrate the data of the online gas analyzer. If the online gas analyzer is abnormal, reduce the measurement interval of the manual gas chromatograph to 5-10 minutes and increase the manual measurement frequency. In order to obtain more accurate measurement parameters, an online gas analyzer and gas chromatograph using helium or argon as the carrier gas can be selected to measure until the nitrogen content of the synthesis gas remains basically unchanged. At this time, the time is t n , let t n The synthesis gas flow rate at the moment is V n The nitrogen content of the synthesis gas is C n , the timing period is t1~t n ;

[0117] Calculate the total nitrogen content in the combustion zone. The nitrogen in the synthesis gas at this time comes from the nitrogen generated by the nitrogen element in the coal and the nitrogen protected by the underground gasifier. The synthesis gas flow rate V(t) in the timing period is multiplied by the nitrogen content of the synthesis gas in the timing period C(t) minus the sum of the nitrogen generated in the coal and the nitrogen protected by the underground gasifier (that is, V n ×C n ), plus the proportion of nitrogen flow rate escaping from the underground gasifier, converted into ammonia and adsorption loss in the total nitrogen content ξ, and then multiplying it by the time dt integral, the total nitrogen content Q (Nm 3 ),Right now:

[0118] Where: Q——Total nitrogen content in the combustion-air zone at the beginning of timing, Nm 3 ;

[0119] V(t)——The flow rate of synthesis gas during the timing period, Nm 3 / h;

[0120] C(t)——Nitrogen content of synthesis gas during the timing period;

[0121] V n ——The flow rate of synthesis gas when the nitrogen content of synthesis gas is stable at the end of the timing, Nm 3 / h;

[0122] C n ——The nitrogen content of the synthesis gas when the nitrogen content of the synthesis gas is stable at the end of the timing;

[0123] ξ——The proportion of nitrogen flow rate escaping from the underground gasifier, converted into ammonia and lost by adsorption to the total nitrogen, which is about 0.5%-3%;

[0124] t1——time when timing starts;

[0125] t n ——The time when the timing ends;

[0126] Obtain the partial pressure P of nitrogen in the combustion-air zone at the end of the timing N ; Since the pressure P and temperature T of the fuel-air zone are always in the detection state, the partial pressure P of nitrogen in the fuel-air zone at the end of the timing N It is equal to the total pressure of the combustion zone P multiplied by the nitrogen content C of the synthesis gas at this time n ,Right now:

[0127] P N =P×C n ;

[0128] Based on P N Get the molar volume V of nitrogen m ; Then the volume of the combustion space is:

[0129]

[0130] Where V is the volume of the combustion space, m 3 ;

[0131] n——the amount of nitrogen, mol,

[0132] Q——Total nitrogen content in the combustion-air zone at the end of the timing, Nm 3 .

[0133] Specifically: After obtaining the partial pressure P of nitrogen in the combustion and air zone N , temperature T and the total nitrogen content Q in the combustion zone, then the appropriate gas state equation can be selected according to the temperature, nitrogen partial pressure and the total nitrogen content in the combustion zone to calculate the total volume of the combustion zone. Under this high temperature and high pressure condition, it is more appropriate to use the Peng-Robinson gas state equation for synthesis gas, and the gas equation expression is:

[0134]

[0135] Where: P N ——Nitrogen partial pressure in the combustion space, Pa;

[0136] R——ideal gas constant, R=8.314J / (mol·K);

[0137] T——absolute temperature of gas in combustion zone, K;

[0138] V m ——The molar volume of nitrogen under these conditions, m3 / mol;

[0139] b——Parameters related to the characteristics of nitrogen substances, Tc——Nitrogen critical temperature, Pc——Nitrogen critical pressure;

[0140]

[0141] c(T)——is a temperature-dependent correction factor,

[0142] Where k = 0.37464 + 1.54226ω - 0.26992ω 2 ;

[0143] Where ω is the eccentricity factor of nitrogen.

[0144] This method measures the volume of the combustion air zone by injecting oxygen to reduce the nitrogen content in the gasifier. It is suitable for projects such as underground coal gasification power generation and urea production where air gasification mode should be selected. The method is implemented for a single underground gasifier, and the change in nitrogen content during the measurement process can be ignored for the total syngas composition of the gasifier group (10-200 gasifiers) produced simultaneously in the industrial project, ensuring that the test process will not affect the normal production of the downstream process.

[0145] Further, this embodiment first describes a method for increasing the nitrogen content, specifically:

[0146] The present invention measures the volume of the combustion zone by injecting air or nitrogen to increase the nitrogen content in the gasifier, and is applicable to projects where a pure oxygen gasification mode is selected for underground coal gasification to produce natural gas, methanol and other chemical products. The method for measuring the volume of the combustion zone of the present invention includes:

[0147] Step S1, when the oxygen gasification mode reaches a stable state, the synthesis gas flow rate is set to V1, and the nitrogen content of the synthesis gas is set to C1. After the oxygen gasification is stabilized, the oxygen supply system reduces the oxygen supply to a preset flow rate, and the air compression station system is turned on to inject air or nitrogen so that the oxygen content of the mixed gas as a gasifying agent reaches 80-90 mol%. Assuming the time at this time is t0, within the range of these oxidant components, the nitrogen content in the synthesis gas will increase from nearly zero to 2-10 mol%. The measurement target value far exceeds the error of the measuring instrument itself. If nitrogen is directly injected during the late shutdown stage of the gasifier, the time to start nitrogen injection is t0.

[0148] Step S2, measuring and calculating the gasification agent flow rate at this time, dividing the length L1 of the injection well gas pipeline by the gasification agent flow rate to obtain the gasification agent injection lag time Δt1, assuming that the time for the gasification agent to reach the combustion zone through the injection well gas pipeline is t'0, then t'0 = t0 + Δt1;

[0149] Step S3, measuring and calculating the flow rate of the synthesis gas at this time, dividing the length L2 from the outlet of the combustion zone to the gas flow meter of the synthesis gas pipeline by the flow rate of the synthesis gas, and obtaining the lag time Δt2 of the synthesis gas. The time when the synthesis gas passes through the synthesis gas pipeline of the product well and reaches the gas flow meter after Δt2 time from time t'0 is t1, and t1=t'0+Δt2;

[0150] Step S4, starting from time t1, the gas flow meter measures and records the synthesis gas flow in real time, the online gas analyzer measures and records the nitrogen content of the synthesis gas in real time, and the manual gas chromatograph measures the composition of the synthesis gas every two hours. If the online gas analyzer is abnormal, the manual gas chromatograph measures the composition of the synthesis gas every half an hour, and the measurement is performed until the nitrogen content of the synthesis gas remains basically unchanged. At this time, the time is t n , let t n The synthesis gas flow rate at the moment is V n The nitrogen content of the synthesis gas is C n , the timing period is t1~t n ;

[0151] Step S5, calculate the total nitrogen content in the combustion zone. The total outflow nitrogen flow rate can be obtained by multiplying the synthesis gas flow rate V(t) in the timing period by the nitrogen content C(t) of the synthesis gas in the timing period and then multiplying it by the time integral. The flow rate of switching to air + oxygen gasification (or pure nitrogen) is V0, then the total input nitrogen flow rate V N2 =V0×C0×ΔT, C0 is the nitrogen content of the injected gasifier, ΔT is the total timing time, then the amount of nitrogen left in the combustion zone is the amount of nitrogen in the injected gas, plus the amount of nitrogen produced by the nitrogen element in the coal and the nitrogen flow rate of the underground gasifier protection. This sum is the nitrogen production when oxygen gasification is stable V1×C1, minus the nitrogen flow rate that escapes in the underground gasifier, is converted into ammonia and is lost by adsorption, which accounts for the proportion of the total nitrogen, minus the amount of nitrogen flowing out of the synthesis gas, then:

[0152]

[0153] Where: Q——Total nitrogen content in the combustion-air zone at the end of the timing, Nm 3 ;

[0154] V0——injection gas flow rate, Nm 3 / h;

[0155] C0——nitrogen content of injected gas;

[0156] V(t)——The flow rate of synthesis gas during the timing period, Nm 3 / h;

[0157] C(t)——Nitrogen content of synthesis gas during the timing period;

[0158] V1——synthetic gas flow rate at the start of timing, Nm 3 / h;

[0159] V n ——The flow rate of synthesis gas at the end of the timing, Nm 3 / h;

[0160] C1——Nitrogen content of synthesis gas at the beginning of timing;

[0161] C n ——Nitrogen content of synthesis gas at the end of timing;

[0162] ΔT——total timing time, h;

[0163] ξ——The proportion of nitrogen flow rate escaping from the underground gasifier, converted into ammonia and lost by adsorption to the total nitrogen, which is approximately 0.5%-3% (determined by laboratory test measurements);

[0164] t1——time when timing starts;

[0165] t n ——The time when the timing ends;

[0166] Step S6, calculate the volume of the combustion zone. Since the pressure P and temperature T of the combustion zone are always in the detection state, the partial pressure P of nitrogen in the combustion zone at the end of the timing is N It is equal to the total pressure of the combustion zone P multiplied by the nitrogen content C of the synthesis gas at this time n ,Right now:

[0167] P N =P×C n

[0168] After obtaining the partial pressure P of nitrogen in the combustion zone N , temperature T and the total nitrogen content Q in the combustion zone, the appropriate gas state equation can be selected according to the temperature, nitrogen partial pressure and the total nitrogen content in the combustion zone to calculate the total volume of the combustion zone. Under this high temperature and high pressure condition, it is more appropriate to use the Peng-Robinson gas state equation for synthesis gas. The gas equation expression is:

[0169]

[0170] Where: P N ——Nitrogen partial pressure in the combustion space, Pa;

[0171] R——ideal gas constant, R=8.314J / (mol·K);

[0172] T——absolute temperature of gas in combustion zone, K;

[0173] Vm ——The molar volume of nitrogen under this condition, m 3 / mol;

[0174] b——Parameters related to the characteristics of nitrogen substances,

[0175] T c ——Nitrogen critical temperature;

[0176] P c ——Nitrogen critical pressure,

[0177] c(T)——is a temperature-dependent correction factor,

[0178] Where k = 0.37464 + 1.54226ω - 0.26992ω 2 ;

[0179] Where ω is the eccentricity factor of nitrogen;

[0180] After obtaining the above data, the molar volume V of nitrogen can be calculated by formula (2): m , then the volume of the combustion void zone is:

[0181]

[0182] Where V is the volume of the combustion space, m 3 ;

[0183] n——the amount of nitrogen, mol,

[0184] Q——Total nitrogen content in the combustion-air zone at the end of the timing, Nm 3 .

[0185] The gas-filled zone data described in the present invention also includes residence time distribution. The method for measuring the gas-filled zone residence time distribution is specifically as follows: injecting air or nitrogen to increase the nitrogen content in the underground gasifier, and recording the DCS process parameters before and after the nitrogen content in the gasifier is increased, respectively, and using these process parameters to calculate the gas-filled zone residence time distribution. The gas-filled zone residence time distribution (RTD) helps to understand and analyze the gasification state of the underground gasifier, guide the design and improvement of the underground gasifier, and can be used to analyze the consumption of reactants in the gas-filled zone, especially the consumption of oxygen and the minimum gas-filled zone value below the explosion limit (LEL), so as to prevent oxygen from directly entering the product well without reaction and mixing with the synthesis gas components to produce an explosive mixture, thereby avoiding production safety problems.

[0186] Specific:

[0187] Step S1, when the oxygen gasification mode reaches a stable state, the oxygen supply system reduces the oxygen supply to a preset flow rate, and the air compression station system is turned on to inject air so that the oxygen content of the mixed gas as a gasifying agent reaches 80-90 mol%. Assuming that the time at this time is t0, within the above-mentioned oxidant composition range, the nitrogen content in the synthesis gas will increase from nearly zero to 2-10 mol%, and the measurement target value far exceeds the error of the measuring instrument itself;

[0188] Step S2, assuming that the gas flow rate of the injected gasifying agent is V0, the nitrogen content of the injected gas is C0, before injecting air and nitrogen, when the oxygen gasification mode reaches a stable state, the synthesis gas flow rate is V1, the nitrogen content of the synthesis gas is C1, then the nitrogen at this time comes from the nitrogen generated by the nitrogen element in the coal and the nitrogen protection of the underground gasifier, which is C1V1, and the mixed gas of air and oxygen is injected at time t0;

[0189] Step S3, measuring and calculating the flow rate of the gasifying agent at this time, dividing the length L1 of the gas pipeline of the injection well by the flow rate of the gasifying agent to obtain the gasifying agent injection lag time Δt1, assuming that the time for the gasifying agent to reach the combustion zone through the gas pipeline of the injection well is t'0, then t'0 = t0 + Δt1;

[0190] Step S4, measuring and calculating the flow rate of the synthesis gas at this time, dividing the length L2 from the outlet of the combustion zone to the gas flow meter of the synthesis gas pipeline by the flow rate of the synthesis gas, and obtaining the lag time Δt2 of the synthesis gas, then the time when the synthesis gas passes through the synthesis gas pipeline of the product well and reaches the gas flow meter after Δt2 time from time t'0 is t1, then t1=t'0+Δt2, and the synthesis gas flow rate and the nitrogen content of the synthesis gas are measured from time t1;

[0191] Step S5, assuming that the nitrogen content of the outlet synthesis gas finally reaches the maximum value C a And it no longer changes, at this time time is t n , the timing ends at this time, and the timing measurement period is t1~t n , assuming t1 = 0, the total time of the timing period ΔT = t n -t1, assuming that the volume of the combustion zone is Q, and the time after t1 = 0 is t (0≤t≤ΔT), then the outlet synthesis gas flow rate is V(t), the nitrogen content is C(t), and the nitrogen concentration in the combustion zone is C'(t), so: C'(0) = C(0), C'(ΔT) = C a ;

[0192] Step S6, at time t, according to the nitrogen balance of the system:

[0193]

[0194] Where: V0——injected gasifying agent flow rate, Nm 3 / h;

[0195] C0——nitrogen content of injected gasifying agent;

[0196] V1——The flow rate of synthesis gas at the beginning of timing (when oxygen gasification is stable), Nm 3 / h;

[0197] C1——Nitrogen content of synthesis gas at the beginning of timing (when oxygen gasification is stable);

[0198] t——the time when the injection of gasifying agent starts, h;

[0199] Q——Volume of the combustion void area, m3, which can be calculated according to the second method for measuring the volume of the combustion void area;

[0200] C'(t)——Nitrogen concentration in the combustion-air zone at time t, Nm 3 / m 3 ;

[0201] V(t)——Export syngas flow rate at time t, Nm 3 / h;

[0202] C(t)——nitrogen content of outlet syngas at time t;

[0203] Step S7, according to the cumulative distribution function of the residence time:

[0204]

[0205] In the formula: ΔT——total timing time;

[0206] Step S8, when t=ΔT, according to formula (3):

[0207]

[0208] Where: C a ——The maximum nitrogen content of the outlet synthesis gas finally reached; Step S9, it is known that:

[0209]

[0210] Where: F(t)——Cumulative distribution function of residence time;

[0211] E(t)——residence time distribution function;

[0212] According to formulas (4), (6) and (7), we have:

[0213]

[0214] Step S10, deriving both sides of formula (8) to obtain:

[0215]

[0216] Step S11, the cumulative distribution function of the residence time is:

[0217]

[0218] Average stay time:

[0219]

[0220] variance:

[0221]

[0222] Step S12, for discrete data, there are:

[0223] Dwell time distribution function:

[0224]

[0225] Cumulative distribution function of residence time:

[0226]

[0227] Average stay time:

[0228]

[0229] variance:

[0230]

[0231] The parameters on the right side of each function in the above step S12 can be obtained by measurement and calculation, so the residence time distribution function, the cumulative distribution function of the residence time, the average residence time and the variance can also be obtained.

[0232] The method for measuring the volume and residence time distribution of the combustion void zone described in the present invention can be used in any stage of an underground coal gasification industrialization project, including early, middle and late operation tests of an underground gasifier. The methods described in the present invention can be arbitrarily combined and cross-checked to obtain accurate data. For example, in the middle stage of underground gasification furnace production, by adjusting the nitrogen content or the corresponding data (method one), when the normal production process is restored, method two can be used to obtain data again for comparison, and vice versa, method two can be used first and then method one to achieve cross-checking, which greatly improves the accuracy of the method of the present invention.

[0233] The measurement and calculation of the combustion void zone volume by the present invention can be used as an assessment of the combustion void zone shape, an assessment of coal consumption, and a reference for the retreat oxygen injection tool. The measurement and calculation of the residence time distribution can be used to understand whether the oxygen in the combustion void zone can be completely reacted and consumed in the combustion void zone. It can also be used to determine the minimum underground coal gasification combustion void zone volume required to completely react all injected oxygen, so as to prevent oxygen from directly entering the product well without reaction and mixing with the synthesis gas components there to produce an explosive mixture, that is, the oxygen content in the synthesis gas is higher than the lower explosion limit (LEL) calculated by the industry. The residence time distribution can also be used as reference data for kinetic research.

Claims

1. A method for measuring combustion air zone data of underground coal gasification, characterized in that: The nitrogen content in the underground gasifier is adjusted, and the combustion zone data is obtained based on the nitrogen content.

2. The method for measuring combustion air zone data for underground coal gasification according to claim 1, characterized in that: in, The fuel-gap area data is fuel-gap area volume data.

3. The method for measuring combustion void area data for underground coal gasification according to claim 2, characterized in that: The adjusting the nitrogen content of the underground gasifier is to reduce the nitrogen content of the underground gasifier.

4. The method for measuring combustion void area data for underground coal gasification according to claim 3, characterized in that: When the air gasification mode reaches a stable state, the synthesis gas flow rate is set to V1, and the nitrogen content of the synthesis gas is set to C1; a gasifying agent with a preset oxygen content is obtained and injected into the combustion and air zone, and the time at this time is recorded as t0; Obtain the gasifying agent flow rate, and divide the length L1 of the injection well gasifying agent pipeline by the gasifying agent flow rate to obtain the gasifying agent injection lag time Δt1. Assuming that the time for the gasifying agent to reach the combustion zone through the injection well gasifying agent pipeline is t'0, then t'0 = t0 + Δt1; Obtain the syngas flow rate, and divide the length L2 from the outlet of the combustion zone to the gas flow meter of the syngas pipeline by the syngas flow rate to obtain the lag time Δt2 of the syngas. Then, the time from t'0 to t1 after Δt2 of the syngas passing through the syngas pipeline of the product well to reach the gas flow meter is t1, so t1=t'0+Δt2; The gas flow meter measures and records the synthesis gas flow rate in real time from time t1 until the nitrogen content of the synthesis gas remains basically unchanged. At this time, the time is t n , let t n The synthesis gas flow rate at the moment is V n The nitrogen content of the synthesis gas is C n , the timing period is t1~t n ; Calculate the total nitrogen content in the combustion zone. Where: Q——Total nitrogen content in the combustion-air zone at the beginning of timing, Nm 3 ; V(t)——The flow rate of synthesis gas during the timing period, Nm 3 / h; C(t)——Nitrogen content of synthesis gas during the timing period; V n ——The flow rate of synthesis gas when the nitrogen content of synthesis gas is stable at the end of the timing, Nm 3 / h; C n ——The nitrogen content of the synthesis gas when the nitrogen content of the synthesis gas is stable at the end of the timing; ξ——Ratio of nitrogen flow rate escaping from underground gasifier, converted into ammonia and lost by adsorption to total nitrogen; t1——time when timing starts; t n ——The time when the timing ends; Obtain the partial pressure P of nitrogen in the combustion-air zone at the end of the timing N ; The partial pressure of nitrogen in the combustion-air zone at the end of the timing P N It is equal to the total pressure of the combustion zone P multiplied by the nitrogen content C of the synthesis gas at this time n ,Right now: P N =P×C n ; Based on P N Get the molar volume V of nitrogen m ; Then the volume of the combustion space is: Where V is the volume of the combustion space, m 3 ; n——the amount of nitrogen, mol, Q——Total nitrogen content in the combustion-air zone at the end of the timing, Nm 3 .

5. The method for measuring combustion void area data for underground coal gasification according to claim 2, characterized in that: The adjusting of the nitrogen content of the underground gasifier is to increase the nitrogen content of the underground gasifier.

6. The method for measuring combustion void area data for underground coal gasification according to claim 5, characterized in that: When the oxygen gasification mode reaches a stable state, let the synthesis gas flow rate be V1, the nitrogen content of the synthesis gas be C1, the oxygen supply system reduces the oxygen supply to a preset flow rate, open the air compressor system to inject air or nitrogen so that the oxygen content of the mixed gas as a gasifying agent reaches a preset percentage, and let the time at this time be t0; if nitrogen is directly injected during the late shutdown stage of the gasifier, the time to start nitrogen injection is t0; Obtain the gasifying agent flow rate, and divide the length L1 of the injection well gasifying agent pipeline by the gasifying agent flow rate to obtain the gasifying agent injection lag time Δt1. Assuming that the time for the gasifying agent to reach the combustion zone through the injection well gasifying agent pipeline is t'0, then t'0 = t0 + Δt1; Obtain the syngas flow rate, and divide the length L2 from the outlet of the combustion zone to the gas flow meter of the syngas pipeline by the syngas flow rate to obtain the lag time Δt2 of the syngas. Then, the time from t'0 to t1 after Δt2 of the syngas passing through the syngas pipeline of the product well to reach the gas flow meter is t1, so t1=t'0+Δt2; The gas flow meter measures and records the synthesis gas flow rate in real time from time t1 until the nitrogen content of the synthesis gas remains basically unchanged. At this time, the time is t n , let t n The synthesis gas flow rate at the moment is V n The nitrogen content of the synthesis gas is C n , the timing period is t1~t n ; Calculate the total nitrogen content in the combustion zone. Where: Q——Total nitrogen content in the combustion-air zone at the end of the timing, Nm 3 ; V0——injection gas flow rate, Nm 3 / h; C0——nitrogen content of injected gas; V(t)——The flow rate of synthesis gas during the timing period, Nm 3 / h; C(t)——Nitrogen content of synthesis gas during the timing period; V1——synthetic gas flow rate at the start of timing, Nm 3 / h; V n ——The flow rate of synthesis gas at the end of the timing, Nm 3 / h; C1——Nitrogen content of synthesis gas at the beginning of timing; C n ——Nitrogen content of synthesis gas at the end of timing; ΔT——total timing time, h; ξ——Ratio of nitrogen flow rate escaping from underground gasifier, converted into ammonia and lost by adsorption to total nitrogen; T1——time when timing starts; t n ——The time when the timing ends; Obtain the partial pressure P of nitrogen in the combustion-air zone at the end of the timing N ; The partial pressure of nitrogen in the combustion-air zone at the end of the timing P N It is equal to the total pressure of the combustion zone P multiplied by the nitrogen content C of the synthesis gas at this time n ,Right now: P N =P×C n ; Based on P N Get the molar volume V of nitrogen m ; Then the volume of the combustion space is: Where V is the volume of the combustion space, m 3 ; n——the amount of nitrogen, mol, Q——Total nitrogen content in the combustion-air zone at the end of the timing, Nm 3 .

7. The method for measuring combustion void area data for underground coal gasification according to claim 4 or 6, characterized in that: in, The molar volume of nitrogen V m The calculation is performed using the Peng-Robinson gas state equation, specifically: Where: P N ——Nitrogen partial pressure in the combustion space, Pa; R——ideal gas constant, R=8.314J / (mol·K); T——absolute temperature of gas in combustion zone, K; V m ——The molar volume of nitrogen under these conditions, m3 / mol; b——Parameters related to the characteristics of nitrogen substances, Tc——Nitrogen critical temperature, Pc——Nitrogen critical pressure; c(T)——is a temperature-dependent correction factor, Where k = 0.37464 + 1.54226ω - 0.26992ω 2 ; Where ω is the eccentricity factor of nitrogen.

8. The method for measuring combustion void area data for underground coal gasification according to claim 5, characterized in that: When the oxygen gasification mode reaches a stable state, the oxygen supply system reduces the oxygen supply to a preset flow rate, and opens the air compressor system to inject air so that the oxygen content of the mixed gas as a gasifying agent reaches a preset value. The time at this time is set as t0; The gas flow rate of the injected gasifier is V0, the nitrogen content of the injected gas is C0, before the injection of air and nitrogen, when the oxygen gasification mode reaches a stable state, the synthesis gas flow rate is V1, the nitrogen content of the synthesis gas is C1, then the nitrogen at this time comes from the nitrogen generated by the nitrogen element in the coal and the nitrogen protection of the underground gasifier, which is V1C1. The mixed gas of air and oxygen is injected at time t0; Obtain the gasifying agent flow rate, and divide the length L1 of the injection well gasifying agent pipeline by the gasifying agent flow rate to obtain the gasifying agent injection lag time Δt1. Assuming that the time for the gasifying agent to reach the combustion zone through the injection well gasifying agent pipeline is t'0, then t'0 = t0 + Δt1; Obtain the syngas flow rate, and divide the length L2 from the outlet of the combustion zone to the gas flow meter of the syngas pipeline by the syngas flow rate to obtain the lag time Δt2 of the syngas. Then, after Δt2 time from time t'0, the time when the syngas passes through the syngas pipeline of the product well and reaches the gas flow meter is t1, and t1=t'0+Δt2. Then, the syngas flow rate and the syngas nitrogen content are measured from time t1; Assume that the nitrogen content of the outlet synthesis gas finally reaches the maximum value Ca and does not change any more. The time at this time is tn. The timing ends at this time. The timing measurement period is t1 to t n , assuming t1 = 0, the total time of the timing period T = t n -t1. Assume that the volume of the combustion zone is Q, and the time after t1 = 0 is t (0≤t≤ΔT), then the outlet synthesis gas flow is V(t), the nitrogen content is C(t), and the nitrogen concentration in the combustion zone is C'(t), so: C'(0) = C(0), C'(ΔT) = C a ; At time t, according to the nitrogen balance of the system: Where: V0——injected gasifying agent flow rate, Nm 3 / h; C0——nitrogen content of injected gasifying agent; V1——synthetic gas flow rate at the start of timing, Nm 3 / h; C1——Nitrogen content of synthesis gas at the beginning of timing; t——the time when the injection of gasifying agent starts, h; Q——combustion space volume, m 3 , can be calculated according to the second method of measuring the volume of the combustion void area; C'(t)——nitrogen concentration in the combustion void area at time t, Nm 3 / m 3 ; V(t)——Export syngas flow rate at time t, Nm 3 / h; C(t)——nitrogen content of outlet synthesis gas at time t; The cumulative distribution function based on the residence time is: Among them, ΔT is the total timing time; When t = ΔT: Where: Ca——the maximum nitrogen content of the outlet synthesis gas; Where, F(t) – cumulative distribution function of residence time; E(t)——residence time distribution function; The cumulative distribution function of the residence time is: Average stay time: variance: For discrete data, we have: Dwell time distribution function: Cumulative distribution function of residence time: Average stay time: variance:

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