Method for evaluating recycle gas utilization efficiency of gas-based direct reduction shaft furnace process

Abstract

The invention discloses a method for evaluating the process recycle gas utilization efficiency of a gas-based direct reduction shaft furnace. The process recycle gas utilization efficiency is calculated by adopting a calculation formula. According to the method, the proportion of the process circulating gas consumed by reduction and carburization after entering the shaft furnace can be intuitively fed back, so that operators and technicians can conveniently judge the conditions of the shaft furnace and observe and compare the working efficiency change condition of the shaft furnace after the shaft furnace input conditions such as pellet raw materials and supply gas components fluctuate and change. The method is simple and convenient in implementation process and easy to apply in industrial scenes; therefore, the reliability of a calculation result is high, and the significance of guiding production is remarkable; the method not only can be used for evaluating the benefit efficiency of the shaft furnace process recycle gas in a certain time period, but also can be used for feeding back an instantaneous value on a control picture of an operating system; when the method is used for calculating the utilization rate of the circulating process gas of the mixed components, the method has more representativeness and guiding significance than single calculation of the utilization rate of H2 or CO.

Description

Technical Field

[0001] The invention relates to the technical field of non-blast furnace ironmaking in metallurgy, in particular to a method for evaluating the utilization efficiency of circulating gas in a gas-based direct reduction shaft furnace process. Background Art

[0002] As the impact of climate warming on human survival and development becomes increasingly obvious, countries around the world are promoting the low-carbon green development strategy of the steel industry. Influenced by this, gas-based direct reduction technology with lower carbon emissions has developed rapidly in recent years. Not only have the gas-based direct reduction plants of Hesteel and Baowu Steel in China been completed and put into production and operation, but gas-based direct reduction projects in the Middle East, North America, North Africa and other places have been approved and entered the construction stage. In addition, world-renowned companies such as Voestalpine, ArcelorMittal, and Nippon Steel are all doing research and development of hydrogen-based direct reduction technology, and plan to build hydrogen-based direct reduction plants in the future to significantly reduce carbon emissions.

[0003] A major feature of gas-based direct reduction technology is that the process gas continuously circulates back and forth in the system; process circulating gas is a unique concept of gas-based direct reduction technology, which means the gas involved in the vertical furnace-related reactions that circulates back and forth in the entire process loop; whenever the process circulating gas enters the vertical furnace, a portion of it will be consumed by reduction and carburization, after which the remaining process circulating gas is subjected to dust removal, dehydration, decarburization, and supplementation of part of the raw gas, and then enters the vertical furnace again after recovery, repeating the cycle over and over again. Based on this feature, each time the process circulating gas enters the vertical furnace, the proportion of the amount consumed by reduction and carburization to the total process circulating gas, that is, the "utilization efficiency of the process circulating gas", is crucial to the entire factory - if the "utilization efficiency of the process circulating gas" is high, then the total flow rate of the process circulating gas under the final equilibrium state will be low, which can greatly save the power consumption of the process circulating gas compressor and the gas consumption of the heating furnace. In addition, it can also reduce the output of furnace dust and reduce the operating costs of the remaining equipment in the entire process loop; otherwise, it will lead to an increase in the power consumption of the process circulating gas compressor and the gas consumption of the heating furnace, and increase the output of furnace dust and the operating costs of the remaining equipment in the entire process loop.

[0004] Since the gas-based direct reduction technology has long been monopolized by foreign countries, there has never been an operating gas-based direct reduction plant in China in the past. Therefore, our understanding and mastery of this type of technology is very poor, and no research on "process cycle gas utilization efficiency" has been involved, nor has any method for evaluating "process cycle gas utilization efficiency" been proposed. After consulting relevant foreign technical materials, no foreign scholars have proposed any method for evaluating the utilization efficiency of gas-based direct reduction shaft furnace process cycle gas.

[0005] In 2023, Hesteel Group put into operation the first gas-based direct reduction plant in China using zero reforming technology. This is also the world's first hydrogen metallurgical plant that uses coke oven gas entirely. Through a year of production practice, our understanding of the gas-based direct reduction process has continued to deepen. Through the combination of theory and practice, we have proposed "a method for evaluating the utilization efficiency of circulating gas in the gas-based direct reduction shaft furnace process" to fill the gap in this field, so that operators and technicians of gas-based direct reduction plants can evaluate and master the operating status of the shaft furnace, and also facilitate latecomers to carry out corresponding technical research in this field. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a method for evaluating the utilization efficiency of circulating gas in a gas-based direct reduction shaft furnace process.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is: the following calculation formula (I) is used to calculate the process cycle gas utilization efficiency:

[0008] Where: Qin: Utilization efficiency of process cycle gas in the selected time period, dimensionless number; Q: The total chemical energy of the make-up gas added to the process loop during the selected time period, in kcal; E: The total chemical energy of the process gas extracted from the process loop during the selected time period, in kcal; F: The total chemical energy of the process gas entering the heating furnace for heating during the selected time period, in kcal.

[0009] Furthermore, when there are multiple injection points for the supply gas, the total chemical energy of the supply gas is the sum of the chemical energies of the supply gas injected from all the injection points.

[0010] Furthermore, when there are multiple extraction points for extracting process gas in the process loop, the total chemical energy of the extracted process gas is the sum of the chemical energy of the process gas extracted from all the extraction points.

[0011] The design concept of the present invention is: in the gas-based direct reduction process, if the process gas entering the furnace is a single-component gas (such as a direct reduction vertical furnace using pure hydrogen), when this method is used for calculation, the influence of the inert gas component and the non-reducible component (N2, H2O, CO2) will be taken into account (affecting the purity, and then affecting the lower heating value LHV of the gas), and the Qin calculation result is more accurate than the utilization rate calculated by simply using the gas flow rate, so it can be well applied to the situation where "the process gas entering the furnace is a single-component gas". If the process gas entering the furnace is a non-single-component gas, including CO, CH4, H2, etc., this method can more comprehensively reflect the proportion of the process gas consumed in carburizing and reduction in the vertical furnace than calculating the utilization rate of a single CO or H2, and it does not need to consider the influence of the complex CH4 conversion process on the CO and H2 components in the furnace, and is more simple and easy to use.

[0012] The beneficial effects of adopting the above technical solution are: First, it can provide intuitive feedback on the proportion of process circulating gas consumed by reduction and carburization after entering the vertical furnace, which is convenient for operators and technicians to judge the furnace condition of the vertical furnace and observe and compare the changes in the working efficiency of the vertical furnace after fluctuations in vertical furnace input conditions such as pellet raw materials and feed gas composition.

[0013] Second, the implementation process of this method is simple and easy to apply in industrial scenarios. This is because the gas components that need to be collected for calculation are basically at room temperature (process) in industrial application scenarios, and are minimally disturbed by factors such as saturated water. The feedback data from the gas analyzer is highly accurate, so the calculation results are highly reliable and have significant significance in guiding production.

[0014] Third, this method can be used to evaluate the efficiency of the vertical furnace process circulating gas within a certain period of time, and can also provide instantaneous value feedback on the control screen of the operating system. When collecting instantaneous values, it is only necessary to link the required reference data, including the instantaneous flow rate, instantaneous low calorific value or instantaneous gas composition of each gas, to the automatic calculation function module.

[0015] Fourth, this method is applicable to both single-component circulating process gas and mixed-component circulating process gas. When used to calculate the utilization rate of mixed-component circulating process gas, it is more representative and instructive than calculating the utilization rate of H2 or CO alone. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0017] Figure 1 It is a flow chart of the gas-based direct reduction process of the present invention.

[0018] In the figure: vertical furnace A; washing, purification and cooling system B; heating furnace C; compressor D; total chemical energy Q1 of the feed gas directly injected from the cone of the vertical furnace; total chemical energy Q2 of the feed gas injected from the process loop; total chemical energy E1 of the process gas extracted from the process loop upstream of the process gas compressor; total chemical energy E2 of the process gas extracted from the process loop downstream of the process gas compressor; total chemical energy F of the process gas entering the heating furnace. DETAILED DESCRIPTION

[0019] Figure 1 As shown, the gas-based direct reduction process adopts the following steps: (1) The process gas generated by the vertical furnace A during the direct reduction process enters the process loop, is washed, purified and cooled by the washing, purification and cooling system B, is compressed by the compressor D, enters the heating furnace C for heating, and is then sent back to the vertical furnace A for direct reduction; (2) The gas-based direct reduction process system is provided with at least one injection point for injecting make-up gas; Figure 1 As shown, there are two injection points, one at the cone of the vertical furnace and one at the process circuit upstream of the heating furnace C; (3) The process loop may be provided with one or more extraction points as required to extract the process gas in the process loop for use as fuel gas for heating furnace or system pressure regulation, etc. Figure 1 There are two extraction points.

[0020] The method for evaluating the utilization efficiency of circulating gas in a gas-based direct reduction shaft furnace process adopts the following steps: (1) Determine the time period t to be evaluated, such as a day, a week, or a few hours; (2) Calculate the average total flow rate fb of the make-up gas corresponding to the time period t to be evaluated, the average total flow rate fc of the process gas extracted from the process loop, and the average flow rate f of the process gas entering the heating furnace.

[0021] The average total flow rate fb of the supply gas is the sum of the average flow rates of the supply gas injected at each injection point; for example Figure 1 In the figure, the average flow rate of the make-up gas directly injected from the cone of the vertical furnace is fb1, and the average flow rate of the make-up gas injected from the process loop is fb2, fb=fb1+fb2.

[0022] The average total flow rate fc of the process gas extracted from the extraction process loop is the sum of the average flow rates of the process gas extracted from each extraction point; for example Figure 1 In the figure, the average flow rate of process gas extracted from the process loop upstream of the process gas compressor is fc1, and the average flow rate of process gas extracted from the process loop downstream of the process gas compressor is fc2, fc=fc1+fc2.

[0023] (3) Calculate the gas lower calorific value LHV, LHVb, and LHVc corresponding to the process gas, supply gas, and extracted process gas entering the heating furnace during the evaluation period. If the gas analyzer configured in the factory cannot feedback the lower calorific value of the supply gas or process gas at each point, the lower calorific value of pure components such as CO, CH4, and H2 can be used to obtain the value by weighted calculation based on the gas components.

[0024] The lower calorific value (kcal / Nm 3 ) multiplied by the corresponding total gas volume (Nm 3 ) to obtain the total chemical energy Q of the supply gas; for example Figure 1 In the formula, the lower calorific value of the make-up gas directly injected from the cone of the vertical furnace is LHVb1, and the total chemical energy of the make-up gas directly injected from the cone of the vertical furnace is Q1=fb1×LHVb1; the lower calorific value of the make-up gas injected from the process loop is LHVb2, and the total chemical energy of the make-up gas injected from the process loop is Q2=fb2×LHVb2; the total chemical energy Q of the make-up gas supplemented into the process loop in the selected time period is Q=(Q1+Q2)×t=(fb1×LHVb1+fb2×LHVb2)×t.

[0025] The lower calorific value (kcal / Nm 3 ) multiplied by the corresponding total gas volume (Nm 3 ) Obtain the total chemical energy E of the extracted process gas; for example Figure 1 In the figure, the lower calorific value of the process gas extracted from the process loop from the upstream of the process gas compressor is LHVc1, and the total chemical energy of the process gas extracted from the process loop from the upstream of the process gas compressor is E1=fc1×LHVc1; the lower calorific value of the process gas extracted from the process loop from the downstream of the process gas compressor is LHVc2, and the total chemical energy of the process gas extracted from the process loop from the downstream of the process gas compressor is E2=fc2×LHVc2; the total chemical energy of the process gas extracted from the process loop in the selected time period is E=(E1+E2)×t=(fc1×LHVc1+fc2×LHVc2)×t.

[0026] (3) Substitute the following calculation formula (I) to calculate the process cycle gas utilization efficiency Qin;

[0027] Where: Qin: Utilization efficiency of process cycle gas in the selected time period, dimensionless number; Q: The total chemical energy of the make-up gas added to the process loop during the selected time period, expressed as the lower calorific value per standard cubic meter of make-up gas (kcal / Nm 3 ) multiplied by the corresponding total gas volume (Nm3 ) is obtained, the unit is kcal; E: The total chemical energy of the process gas extracted from the process loop during the selected time period, expressed as the lower calorific value per standard cubic meter of process gas extracted (kcal / Nm 3 ) multiplied by the corresponding total gas volume (Nm 3 ) is obtained, the unit is kcal; F: The total chemical energy F of the process gas entering the heating furnace during the selected time period, expressed as the lower calorific value per standard cubic meter of process gas (kcal / Nm 3 ) multiplied by the corresponding total gas volume (Nm 3 ) is obtained, the unit is kcal.

[0028] Since the selected time period (t) is equal, "average flow rate × gas corresponding lower heating value LHV" can be directly used instead of Q / E / F; for example Figure 1 As shown, the calculation formula is as follows: Qin=((fb1×LHVb1+fb2×LHVb2)×t-(fc1×LHVc1+fc2×LHVc2)×t) / (f×LHV×t)×100%=((fb1×LHVb1+fb2×LHVb2)-(fc1×LHVc1+fc2×LHVc2)) / (f×LHV) ×100%. Example

[0029] Taking a direct reduction plant of a leading domestic steel company that uses a variety of raw materials as feed gas as an example, the utilization efficiency of the process circulating gas in a certain shift of the plant's vertical furnace for 12 hours was calculated.

[0030] The plant uses three types of make-up gas, namely natural gas, coke oven gas and green hydrogen, which are injected into the process loop from different locations, all before the process circulating gas enters the heating furnace; there is only one process gas extracted from the process loop, which is the process tail gas upstream of the process gas compressor, used for top pressure control. The specific process is shown in the figure above.

[0031] During the 12-hour shift, the process gas flow rate entering the heating furnace for heating is 180,000 Nm 3 / h; the injected supplementary gas is coke oven gas 30000Nm 3 / h, hydrogen 4000Nm 3 / h, natural gas 10000Nm 3 / h; the flow rate of the extracted process gas is 19000Nm 3 / h.

[0032] The factory is equipped with a mass spectrometer, which can feedback and collect the gas composition at each point. The gas components collected by the mass spectrometer in the corresponding time period are shown in Table 1.

[0033]

[0034] According to the gas components in Table 1 above, the lower calorific value corresponding to the gas components is calculated according to the weighted algorithm, and the average flow rate of each gas in the corresponding time period is statistically shown in Table 2.

[0035]

[0036] According to the above method, the utilization efficiency Qin of the circulating gas in the direct reduction shaft furnace process in this shift is calculated as: Qin=((4000×2574.42+10000×8580.05+30000×3979.06)-(19000×3005.27)) / (180000×2967.51)×100%=29.6488% That is, in this shift, the utilization efficiency of the circulating gas of the direct reduction vertical furnace process is Qin = 29.6488%.

Claims

1. A method for evaluating the utilization efficiency of circulating gas in a gas-based direct reduction shaft furnace process, characterized in that: The following calculation formula (I) is used to calculate the process cycle gas utilization efficiency: （Ⅰ） Where: Qin: Utilization efficiency of process cycle gas in the selected time period, dimensionless number; Q: The total chemical energy of the make-up gas added to the process loop during the selected time period, in kcal; E: The total chemical energy of the process gas extracted from the process loop during the selected time period, in kcal; F: The total chemical energy of the process gas entering the heating furnace for heating during the selected time period, in kcal.

2. The method for evaluating the utilization efficiency of circulating gas in a gas-based direct reduction shaft furnace process according to claim 1, characterized in that: When there are multiple injection points for the supply gas, the total chemical energy of the supply gas is the sum of the chemical energies of the supply gas injected from all the injection points.

3. A method for evaluating the utilization efficiency of circulating gas in a gas-based direct reduction shaft furnace process according to claim 1 or 2, characterized in that: When there are multiple extraction points for extracting process gas in the process loop, the total chemical energy of the extracted process gas is the sum of the chemical energies of the process gas extracted from all the extraction points.

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