Method for continuous combustion of low oxygen excess air coupled with low calorific value gas for heating rolling

Abstract

This invention discloses a method and system for continuous combustion of low-oxygen-enriched air and low-calorific-value gas in steel rolling. The method includes: preheating the low-oxygen-enriched air and low-calorific-value gas to a target temperature, wherein the target temperature is 350-450°C, the oxygen content of the low-oxygen-enriched air is 24-30%, and the calorific value of the low-calorific-value gas is 1000-1200 kcal / m³. 3 The method involves supplying preheated, low-oxygen-enriched air and low-calorific-value coal gas to the furnace chamber for continuous combustion to heat the steel billets entering the furnace. Based on this method, the combustion temperature of low-calorific-value coal gas under continuous combustion conditions can reach the steel rolling heating temperature, thus solving the problem that the combustion temperature of low-calorific-value coal gas under continuous combustion is too low to be used for steel rolling heating. This allows for a replacement of regenerative heating furnace technology and solves the process and structural coal gas emission problems associated with the gas reversal process in regenerative heating furnace technology.

Description

Technical Field

[0001] This invention relates to the field of steel production, and more particularly to a method and system for heating steel rolling by coupled continuous combustion of low-oxygen-enriched air and low-calorific-value gas. Background Technology

[0002] Heating steel billets in the rolling mill process requires a large amount of gas to provide high-temperature heat energy. The United Steel Corporation generates a significant amount of low-calorific-value gas during its production process, such as blast furnace gas and converter gas. Because the combustion temperature of low-calorific-value gas under conventional combustion methods does not meet the basic requirements of the rolling mill heating furnace, the United Steel Corporation employs a dual regenerative combustion method using both air and gas to increase the combustion temperature of the low-calorific-value gas. This dual regenerative technology ensures that the low-calorific-value gas fully meets the basic requirements of the billet heating process in the rolling mill. Currently, over 95% of the rolling mill processes at the United Steel Corporation utilize this dual regenerative gas heating furnace technology.

[0003] However, existing low-calorific-value gas dual regenerative heating furnace technology has serious technical defects. Because the regenerative burners in the regenerative heating furnace have combustion reversal, when the regenerative burner on the combustion side switches from combustion to flue gas emission, the residual gas in the gas reversing valve to the regenerator pipe on that side will flow in the opposite direction and be emitted into the atmosphere with the flue gas. This leads to the following four adverse consequences: 1) Each switch releases a large amount of toxic gas into the atmosphere, causing very serious process emissions of toxic and harmful CO gases, severely polluting the ecological environment; 2) The sealing structure of the gas three-way valve controlling the combustion switching action is frequently damaged, causing a large amount of gas to leak into the flue gas, resulting in very serious structural emissions of toxic and harmful CO gases, severely polluting the ecological environment; 3) The large-scale process and structural release of gas causes a serious waste of high-quality gas energy and leads to a large amount of additional greenhouse gas emissions; 4) The gas three-way valve's poor sealing often causes the CO concentration in the furnace area to exceed the standard, resulting in a very poor working environment for the steel rolling furnace operators. It is estimated that regenerative rolling mill heating furnaces in my country waste approximately 12 billion standard cubic meters of high-quality, low-calorific-value coal gas annually and release approximately 3.3 billion standard cubic meters of toxic and harmful CO gas, resulting in severe environmental pollution and energy waste. For a long time, these problems have remained unresolved worldwide, becoming a technological bottleneck restricting the green and low-carbon transformation of the rolling mill process. Summary of the Invention

[0004] One object of the present invention is to solve at least the above-mentioned problems and / or defects, and to provide at least the advantages described below.

[0005] The purpose of this invention is to provide a steel rolling heating method and system for coupled continuous combustion of low-oxygen-enriched air and low-calorific-value coal gas. This method enables the combustion temperature of low-calorific-value coal gas under continuous combustion conditions to meet the steel rolling heating temperature, fundamentally solving the technical problem that the combustion temperature of low-calorific-value coal gas is too low for continuous combustion and cannot be applied to steel rolling heating. This method can replace the existing regenerative heating furnace technology and solve the problems of process and structural coal gas emissions in the gas reversal process of regenerative heating furnace technology.

[0006] Firstly, a method for heating steel rolling involving the coupled continuous combustion of low-oxygen-enriched air and low-calorific-value gas is provided, comprising:

[0007] Low-oxygen-enriched air and low-calorific-value coal gas are preheated to a target temperature, wherein the target temperature is 350–450°C, the oxygen content of the low-oxygen-enriched air is 24–30%, and the calorific value of the low-calorific-value coal gas is 1000–1200 kcal / m³. 3 ;

[0008] Low-oxygen-enriched air and low-calorific-value gas, preheated to the target temperature, are delivered to the furnace chamber of the heating furnace for continuous combustion to heat the steel billet entering the furnace chamber.

[0009] Preferably, in the steel rolling heating method of coupled continuous combustion of low oxygen-enriched air and low calorific value gas, the low calorific value gas is a mixture of blast furnace gas and converter gas, or a mixture of blast furnace gas and natural gas, or a mixture of blast furnace gas and coke oven gas.

[0010] Preferably, in the steel rolling heating method of coupled continuous combustion of low oxygen-enriched air and low calorific value gas, the furnace chamber of the heating furnace includes a preheating section, a heating section and a homogenizing section arranged in sequence according to the order in which the steel billet passes after entering the furnace, and the flow direction of the high-temperature flue gas generated by the combustion of the low oxygen-enriched air and the low calorific value gas is from the homogenizing section and the heating section to the preheating section.

[0011] The process of supplying preheated, low-oxygen-enriched air and low-calorific-value gas to the furnace chamber for continuous combustion to heat the steel billet entering the furnace chamber includes:

[0012] Preheated air with low oxygen content and low calorific value gas to the target temperature are transported to the homogenization section and the heating section for continuous combustion.

[0013] The low-oxygen-enriched air and the high-temperature flue gas generated by the combustion of low-calorific-value coal gas, which are preheated to the target temperature, flow to the preheating section to preheat the steel billet entering the preheating section.

[0014] As the steel billet sequentially enters the heating section and the soaking section from the preheating section, the steel billet is heated sequentially by the continuous combustion of low-oxygen-enriched air and low-calorific-value coal gas preheated to the target temperature in the heating section and the soaking section.

[0015] Preferably, in the steel rolling heating method of coupled continuous combustion of low-oxygen-enriched air and low-calorific-value gas, the preheating of the low-oxygen-enriched air and low-calorific-value gas to the target temperature includes:

[0016] The low-oxygen-enriched air and the low-calorific-value gas are preheated to the target temperature using the medium-temperature flue gas flowing out of the furnace chamber. The medium-temperature flue gas is formed by the high-temperature flue gas flowing to the preheating section and preheating the steel billet entering the preheating section before cooling it down.

[0017] Preferably, in the steel rolling heating method of coupled continuous combustion of low oxygen-enriched air and low calorific value gas, the flue gas outlet side of the heating furnace is provided with a hot water or saturated steam production device, a high-temperature air preheater, a high-temperature gas preheater, a low-temperature air preheater, and a low-temperature gas preheater. The high-temperature air preheater and the high-temperature gas preheater are arranged side by side on the flue gas outlet side of the hot water or saturated steam production device, the low-temperature air preheater is arranged on the flue gas outlet side of the high-temperature air preheater, and the low-temperature gas preheater is arranged on the flue gas outlet side of the high-temperature gas preheater.

[0018] The step of preheating the low-oxygen-enrichment air and the low-calorific-value coal gas to the target temperature using the medium-temperature flue gas includes:

[0019] The intermediate-temperature flue gas is transported to a hot water or saturated steam production device to produce hot water or saturated steam, thereby cooling the intermediate-temperature flue gas into sub-intermediate-temperature flue gas.

[0020] Low-oxygen-enriched air and low-calorific-value coal gas that have been preheated at low temperature are respectively transported to the high-temperature air preheater and the high-temperature coal gas preheater. The intermediate-temperature flue gas is transported to the high-temperature air preheater and the high-temperature coal gas preheater. The intermediate-temperature flue gas is used to preheat the low-oxygen-enriched air and low-calorific-value coal gas that have been preheated at low temperature to the target temperature.

[0021] Unpreheated low-oxygen-enriched air and low-calorific-value coal gas are respectively fed to the low-temperature air preheater and the low-temperature coal gas preheater. The intermediate-temperature flue gas flowing out of the high-temperature air preheater and the high-temperature coal gas preheater is fed to the low-temperature air preheater and the low-temperature coal gas preheater. The intermediate-temperature flue gas flowing out of the high-temperature air preheater and the high-temperature coal gas preheater are used to preheat the unpreheated low-oxygen-enriched air and low-calorific-value coal gas to 250-300°C.

[0022] Preferably, in the steel rolling heating method of coupled continuous combustion of low-oxygen-enriched air and low-calorific-value gas, a flue gas purification device is provided on the flue gas outlet side of the high-temperature air preheater and the high-temperature gas preheater, and the low-temperature air preheater and the low-temperature gas preheater are located on the flue gas outlet side of the flue gas purification device; the method further includes:

[0023] The secondary and intermediate temperature flue gas flowing out of the high-temperature air preheater and the high-temperature gas preheater is transported to the flue gas purification device for purification.

[0024] Secondly, a steel rolling heating system is provided that involves the continuous combustion of low-oxygen-enriched air and low-calorific-value gas, comprising:

[0025] A preheating system is used to preheat low-oxygen-enriched air and low-calorific-value coal gas to a target temperature, wherein the target temperature is 350–450°C, the oxygen content of the low-oxygen-enriched air is 24–30%, and the calorific value of the low-calorific-value coal gas is 1000–1200 kcal / m³. 3 ;

[0026] The furnace chamber of the heating furnace includes a preheating section, a heating section, and a soaking section arranged sequentially according to the order in which the steel billet passes after entering the furnace. The soaking section and the heating section are each equipped with a combustion device connected to the preheating system. This device supplies low-oxygen-enriched air and low-calorific-value gas, preheated to the target temperature, to the soaking section and the heating section for continuous combustion, thereby heating the steel billet entering the heating section and the soaking section. The preheating section is provided with a flue gas outlet, ensuring that the high-temperature flue gas generated by the combustion of the low-oxygen-enriched air and the low-calorific-value gas flows from the soaking section and the heating section towards the preheating section, preheating the steel billet upon reaching the preheating section.

[0027] Preferably, in the steel rolling heating system of coupled continuous combustion of low oxygen-enriched air and low calorific value gas, at least two combustion devices are symmetrically arranged in the soaking section and at least two combustion devices are symmetrically arranged in the heating section.

[0028] Preferably, in the steel rolling heating system of coupled continuous combustion of low-oxygen-enriched air and low-calorific-value gas, the preheating system includes:

[0029] A hot water or saturated steam production device, connected to the flue gas outlet of the preheating section, is used to supply medium-temperature flue gas to produce hot water or saturated steam and to cool the medium-temperature flue gas to a sub-medium-temperature flue gas, wherein the medium-temperature flue gas is formed by the high-temperature flue gas flowing to the preheating section and preheating the steel billet entering the preheating section before cooling it down.

[0030] A high-temperature air preheater is installed on the flue gas outlet side of the hot water or saturated steam production device. It is used to supply low-oxygen-enriched air that has been preheated at low temperature and the secondary medium-temperature flue gas to it, and to use the secondary medium-temperature flue gas to preheat the low-oxygen-enriched air that has been preheated at low temperature to the target temperature.

[0031] A high-temperature gas preheater is installed on the flue gas outlet side of the hot water or saturated steam production device. It is used to supply low-calorific-value gas that has been preheated at low temperature and the secondary medium-temperature flue gas to it, and to use the secondary medium-temperature flue gas to preheat the low-calorific-value gas that has been preheated at low temperature to the target temperature.

[0032] A low-temperature air preheater is installed on the flue gas outlet side of the high-temperature air preheater. It is used to supply unpreheated low-oxygen-enriched air and secondary medium-temperature flue gas flowing out of the high-temperature air preheater and the high-temperature gas preheater to it. The secondary medium-temperature flue gas flowing out of the high-temperature air preheater and the high-temperature gas preheater is used to preheat the unpreheated low-oxygen-enriched air to 250-300°C.

[0033] A low-temperature gas preheater is installed on the flue gas outlet side of the high-temperature gas preheater. It is used to supply unpreheated low-calorific-value gas and the secondary medium-temperature flue gas flowing out of the high-temperature air preheater and the high-temperature gas preheater to it. The secondary medium-temperature flue gas flowing out of the high-temperature air preheater and the high-temperature gas preheater is used to preheat the unpreheated low-calorific-value gas to 250-300°C.

[0034] Preferably, in the steel rolling heating system of coupled continuous combustion of low-oxygen-enriched air and low-calorific-value gas, the preheating system further includes:

[0035] A flue gas purification device is installed on the flue gas outlet side of the high-temperature air preheater and the high-temperature gas preheater. The low-temperature air preheater and the low-temperature gas preheater are installed on the flue gas outlet side of the flue gas purification device. The device is used to supply the secondary and intermediate temperature flue gas flowing out of the high-temperature air preheater and the high-temperature gas preheater to the device and to purify the secondary and intermediate temperature flue gas flowing out of the high-temperature air preheater and the high-temperature gas preheater.

[0036] The present invention has at least the following beneficial effects:

[0037] This invention provides a method and system for continuous combustion of low-oxygen-enriched air and low-calorific-value coal gas in steel rolling. The method includes: preheating the low-oxygen-enriched air and low-calorific-value coal gas to a target temperature, wherein the target temperature is 350–450°C, the oxygen content of the low-oxygen-enriched air is 24–30%, and the calorific value of the low-calorific-value coal gas is 1000–1200 Kcal / m³. 3The method involves preheating low-oxygen-enriched air and low-calorific-value gas to the target temperature and then continuously burning them in the furnace to heat the steel billets entering the furnace. Based on this method and system, by preheating the low-calorific-value gas and low-oxygen-enriched air to the target temperature to compensate for their temperature, the heat loss during continuous combustion of the low-calorific-value gas is reduced. This allows the combustion temperature of the low-calorific-value gas under continuous combustion conditions to reach the steel rolling heating temperature, fundamentally solving the technical problem of low combustion temperature of low-calorific-value gas under continuous combustion, which prevents its application in steel rolling heating. This replaces existing regenerative heating furnace technology and solves the process and structural gas emission problems associated with the gas reversal process in regenerative heating furnace technology.

[0038] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0039] Figure 1 This is a flowchart of the steel rolling heating method for continuous combustion of low-oxygen-enriched air and low-calorific-value gas according to an embodiment of the present invention.

[0040] Figure 2 This is a schematic diagram of the structure of the steel rolling heating system for continuous combustion of low-oxygen-enriched air and low-calorific-value gas, as described in an embodiment of the present invention. Detailed Implementation

[0041] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0042] Figure 1 This is a flowchart of a steel rolling heating method for continuous combustion of low-oxygen-enriched air and low-calorific-value gas, as described in an embodiment of the present invention. Figure 2 This is a schematic diagram of the steel rolling heating system for continuous combustion of low-oxygen-enriched air and low-calorific-value gas, as described in an embodiment of the present invention. The following is in conjunction with... Figure 2 This invention describes a steel rolling heating method involving the continuous combustion of low-oxygen-enriched air and low-calorific-value coal gas. For example... Figure 1 and Figure 2 As shown, this invention provides a steel rolling heating method for continuous combustion of low-oxygen-enriched air and low-calorific-value gas, comprising:

[0043] Step 110: Preheat the low-oxygen-enriched air and low-calorific-value coal gas to a target temperature, wherein the target temperature is 350–450°C, the oxygen content of the low-oxygen-enriched air is 24–30%, and the calorific value of the low-calorific-value coal gas is 1000–1200 Kcal / m³. 3 .

[0044] Step 120: Low-oxygen-enriched air and low-calorific-value gas, preheated to the target temperature, are delivered to the furnace chamber 210 of the heating furnace for continuous combustion to heat the steel billet entering the furnace chamber 210.

[0045] This invention, through preheating low-calorific-value coal gas and low-oxygen-enriched air to a target temperature, compensates for the temperature loss during continuous combustion of the low-calorific-value coal gas, thereby enabling the combustion temperature of the low-calorific-value coal gas under continuous combustion conditions to reach the steel rolling heating temperature. Specifically, the combustion temperature of the preheated low-oxygen-enriched air and low-calorific-value coal gas in the furnace can reach approximately 1300°C, achieving steel rolling heating. In other words, this invention, by synergistically combining the calorific value of the low-calorific-value coal gas, the oxygen enrichment of the low-oxygen-enriched air, and the preheating temperature, improves the combustion temperature of the low-calorific-value coal gas under continuous combustion, making it able to meet the heating requirements of steel rolling. Based on this, the embodiments of the present invention fundamentally solve the technical problem that the combustion temperature of low-calorific-value coal gas is low under continuous combustion mode, making it unsuitable for steel rolling heating. It can replace the existing regenerative heating furnace technology and solve the problems of process and structural coal gas emissions in the gas reversal process of regenerative heating furnace technology.

[0046] In some examples, the target temperature is preferably 450°C.

[0047] In some embodiments, the low-oxygen-enriched air can be prepared by mixing air with pure oxygen, or by using a membrane method or a pressure swing adsorption device. This embodiment of the invention does not specifically limit the method. The oxygen content of the low-oxygen-enriched air is preferably 25%.

[0048] In some embodiments, the low-calorific-value gas is prepared by mixing blast furnace gas and converter gas, or by mixing blast furnace gas and natural gas, or by mixing blast furnace gas and coke oven gas. When preparing low-calorific-value gas by mixing blast furnace gas and converter gas, the mixing ratio of blast furnace gas to converter gas can be 2:1.

[0049] In some embodiments, the amounts of low-oxygen-enriched air and low-calorific-value coal gas can be calculated based on the chemical reaction equation between O2 and CO. Generally, to ensure sufficient reaction of CO in the low-calorific-value coal gas, the amount of O2 used must be controlled to be appropriately excessive. In some examples, the volume ratio of low-oxygen-enriched air to low-calorific-value coal gas is 0.7 to 0.8.

[0050] In some embodiments, in the steel rolling heating system, the furnace chamber 210 includes a preheating section 213, a heating section 212, and a soaking section 211 arranged sequentially according to the order in which the steel billet passes after entering the furnace. The flow direction of the high-temperature flue gas generated by the combustion of the low-oxygen-enriched air and the low-calorific-value gas is from the soaking section 211 and the heating section 212 to the preheating section 213. The step of conveying the low-oxygen-enriched air and low-calorific-value gas preheated to the target temperature to the furnace chamber for continuous combustion to heat the steel billet entering the furnace chamber includes: conveying the low-oxygen-enriched air and low-calorific-value gas preheated to the target temperature to the furnace chamber for continuous combustion. Low-calorific-value gas is transported to the homogenization section 211 and the heating section 212 for continuous combustion; the low-oxygen-enriched air preheated to the target temperature and the high-temperature flue gas generated by the combustion of the low-calorific-value gas flow to the preheating section 213 to preheat the steel billet entering the preheating section 213; as the steel billet enters the heating section 212 and the homogenization section 211 sequentially from the preheating section 213, the low-oxygen-enriched air preheated to the target temperature and the low-calorific-value gas are used to heat the steel billet entering the heating section 212 and the homogenization section 211 in sequence through continuous combustion in the heating section 212 and the homogenization section 211.

[0051] Specifically, the furnace chamber is divided into three heating sections according to different furnace temperature levels: a preheating section 213, a heating section 212, and a soaking section 211. Based on this configuration, the heating process of the rolled steel billet is as follows: the billet enters the furnace chamber 210 through the inlet end of the preheating section 213, and then passes through the preheating section 213, the heating section 212, and the soaking section 211 in sequence. When the billet reaches the required heating temperature, it exits the furnace chamber 210 through the outlet end of the soaking section. The heating section 212 utilizes the heat generated by the continuous combustion of low-oxygen-enriched air and low-calorific-value gas preheated to the target temperature to rapidly heat the billet. The soaking section 211 utilizes the heat generated by the continuous combustion of low-oxygen-enriched air and low-calorific-value gas preheated to the target temperature to soak the billet, reducing the temperature difference across the billet cross-section. The preheating section 213 utilizes the residual heat from the high-temperature section of the high-temperature flue gas leaving the heating and soaking sections to preheat the billet, while simultaneously achieving efficient recovery of the residual heat from the high-temperature section of the flue gas.

[0052] In some examples, combustion devices 214 (specifically, burners) are arranged in the heating section 212 and the soaking section 211, respectively, while no combustion device is provided in the preheating section 213. Low-oxygen-enriched air and low-calorific-value gas, preheated to the target temperature, are injected into the furnace through different channels of the combustion devices 214 for continuous diffusion combustion. The combustion products release heat to the steel billet, heating it. Furthermore, the combustion devices 214 in both the heating and soaking sections are symmetrically arranged.

[0053] Corresponding to the billet heating process, the flow process of flue gas in the furnace is as follows: Low-oxygen-enriched air and low-calorific-value gas, preheated to the target temperature, are combusted in the heating section 212 and the soaking section 211. The combustion products release heat to the billet, forming high-temperature flue gas, which can reach 800–1000℃. This high-temperature flue gas flows to the preheating section 213, where it preheats the billet. It then exits from the flue gas outlet of the preheating section 213, forming medium-temperature flue gas, with a temperature of 600–800℃.

[0054] In some embodiments, preheating the low-oxygen-enriched air and low-calorific-value gas to the target temperature includes: using medium-temperature flue gas flowing out of the furnace chamber 210 of the heating furnace to preheat the low-oxygen-enriched air and the low-calorific-value gas to the target temperature, wherein the medium-temperature flue gas is formed by the high-temperature flue gas flowing to the preheating section 213 and preheating the steel billet entering the preheating section 213 and then cooling it down.

[0055] Using medium-temperature flue gas to preheat low-oxygen-enriched air and low-calorific-value coal gas can achieve both preheating of these gases and waste heat recovery from the medium-temperature flue gas.

[0056] In some examples, combined Figure 2The steel rolling heating system shown is a continuous combustion system of low-oxygen-enriched air and low-calorific-value gas. The furnace chamber 210 is equipped with a hot water or saturated steam production device 221, a high-temperature air preheater 222, a high-temperature gas preheater 223, a low-temperature air preheater 225, and a low-temperature gas preheater 224 on the flue gas outlet side. The high-temperature air preheater 222 and the high-temperature gas preheater 223 are arranged side by side on the flue gas outlet side of the hot water or saturated steam production device 221. The low-temperature air preheater 225 is arranged on the flue gas outlet side of the high-temperature air preheater 222. The low-temperature gas preheater 224 is arranged on the flue gas outlet side of the high-temperature gas preheater 223. The step of preheating the low-oxygen-enriched air and the low-calorific-value coal gas to a target temperature using the medium-temperature flue gas includes: conveying the medium-temperature flue gas to a hot water or saturated steam production device 221 to produce hot water or saturated steam, thereby cooling the medium-temperature flue gas to a sub-medium-temperature flue gas; conveying the low-oxygen-enriched air and low-calorific-value coal gas, which have been preheated at low temperatures, to the high-temperature air preheater 222 and the high-temperature coal gas preheater 223, respectively; conveying the sub-medium-temperature flue gas to the high-temperature air preheater 222 and the high-temperature coal gas preheater 223; and using the sub-medium-temperature flue gas to preheat the low-oxygen-enriched air and low-calorific-value coal gas, which have been preheated at low temperatures, to the target temperature. Air and low-calorific-value coal gas are preheated to the target temperature at high temperature; unpreheated low-oxygen-enriched air and low-calorific-value coal gas are respectively transported to the low-temperature air preheater 225 and the low-temperature coal gas preheater 224; the intermediate-temperature flue gas flowing out of the high-temperature air preheater 222 and the high-temperature coal gas preheater 223 is transported to the low-temperature air preheater 225 and the low-temperature coal gas preheater 224; the unpreheated low-oxygen-enriched air and low-calorific-value coal gas are preheated to 250-300°C at low temperature using the intermediate-temperature flue gas flowing out of the high-temperature air preheater 222 and the high-temperature coal gas preheater 223.

[0057] The temperature of the medium-temperature flue gas can reach 600–800℃, while the target temperature for low-oxygen-enriched air and low-calorific-value coal gas is only 350–450℃, resulting in a significant temperature difference. To improve the efficiency of waste heat recovery, the medium-temperature flue gas is first used to produce hot water or superheated steam, recovering a portion of its waste heat. After this stage of waste heat recovery, the medium-temperature flue gas cools down to become secondary medium-temperature flue gas, with a temperature of 400–600℃, which perfectly meets the preheating requirements for low-oxygen-enriched air and low-calorific-value coal gas. This secondary medium-temperature flue gas can then be used to further preheat the low-oxygen-enriched air and low-calorific-value coal gas. Furthermore, a two-stage preheating method is employed for the low-oxygen-enriched air and low-calorific-value coal gas, progressively raising their temperatures to the target temperature. This two-stage preheating method offers high preheating efficiency and effectively achieves the required target temperature.

[0058] This invention enables four-stage recovery of waste heat from flue gas. Stage 1: The high-temperature waste heat from the high-temperature flue gas is used to preheat the steel billet entering the furnace; the heat exchange process is completed in the furnace preheating section 213. Stage 2: Medium-temperature flue gas is used to heat the working fluid water or saturated steam in the hot water or saturated steam production device 221 to produce hot water or superheated steam. Stage 3: Sub-medium-temperature flue gas is used in the high-temperature gas preheater 223 to raise the temperature of low-calorific-value gas from the low-temperature gas preheater 224 to the target temperature, and in the high-temperature air preheater 222 to raise the temperature of low-oxygen-enriched air from the low-temperature air preheater 225 to the target temperature. Stage 4: The low-temperature waste heat from the sub-medium-temperature flue gas is used in the low-temperature gas preheater 224 to preheat the low-calorific-value gas, and in the low-oxygen-enriched air preheater 225 to preheat the low-oxygen-enriched air.

[0059] In some examples, a flue gas purification device 226 is provided on the flue gas outlet side of the high-temperature air preheater 222 and the high-temperature gas preheater 223, and the low-temperature air preheater 225 and the low-temperature gas preheater 224 are provided on the flue gas outlet side of the flue gas purification device 226. The method further includes: conveying the sub-medium-temperature flue gas flowing out of the high-temperature air preheater 222 and the high-temperature gas preheater 223 to the flue gas purification device 226 for purification.

[0060] Specifically, the process of preheating low-oxygen-enriched air and low-calorific-value coal gas using medium-temperature flue gas, i.e., the process of waste heat recovery from medium-temperature flue gas, is as follows:

[0061] The intermediate-temperature flue gas first enters the heat exchange surface of the waste heat boiler, where the higher-temperature portion of the waste heat is used to supply hot water or saturated steam, producing hot water or superheated steam. When producing hot water, the waste heat boiler heat exchange surface can be an external economizer of a high-parameter power generation boiler's intermediate-pressure supplementary steam superheater or a vaporization cooling device; when producing superheated steam, the waste heat boiler heat exchange surface can be a steam superheater. The flue gas leaving the waste heat boiler heat exchange surface is classified as secondary intermediate-temperature flue gas.

[0062] The intermediate-temperature flue gas is then split into intermediate-temperature air-flue gas and intermediate-temperature coal-smoke gas. The intermediate-temperature air-flue gas enters the high-temperature air preheater 222 to preheat the low-oxygen-enriched air at high temperature, and the flue gas leaving the high-temperature air preheater 222 is the air-flue gas to be purified. The intermediate-temperature coal-smoke gas enters the high-temperature coal gas preheater 223 to preheat the low-calorific-value coal gas at high temperature, and the flue gas leaving the high-temperature coal gas preheater 223 is the coal-smoke gas to be purified. The low-oxygen-enriched air and low-calorific-value coal gas, after high-temperature preheating, reach the target temperature and can be transported to the furnace 210 of the heating furnace for continuous combustion. Here, the composition and temperature of the intermediate-temperature air-flue gas and the intermediate-temperature coal-smoke gas are the same; the different names are only for descriptive convenience. Similarly, the composition and temperature of the air-flue gas to be purified and the coal-smoke gas to be purified are also the same; the different names are only for descriptive convenience.

[0063] The coal smoke to be purified and the air smoke to be purified are mixed and then enter the flue gas purification device 226 for purification, forming purified flue gas. Subsequently, the purified flue gas is again divided into purified coal smoke and purified air smoke. The flue gas purification device can be a desulfurization, dust removal, and denitrification purification device. The purification sequence adopted is sodium bicarbonate desulfurization, bag filter dust collection, and SCR denitrification. Here, the composition and temperature of the purified air smoke and purified coal smoke are the same; the different names are only for descriptive convenience.

[0064] The purified coal smoke then enters the low-temperature gas preheater 224 to preheat the low-calorific-value gas at a low temperature. The flue gas leaving the low-temperature gas preheater 224 is the coal smoke exhaust. The purified air exhaust then enters the low-oxygen-enriched air preheater 225 to preheat the low-oxygen-enriched air at a low temperature. The flue gas leaving the low-temperature air preheater 225 is the air exhaust. The coal smoke exhaust and air exhaust are then mixed to form mixed smoke exhaust. The temperature of the low-oxygen-enriched air and low-calorific-value gas, after low-temperature preheating, reaches 250-300℃. The mixed smoke exhaust is discharged into the atmosphere through the induced draft fan 228 and the chimney. Here, the composition and temperature of the coal smoke exhaust and the controlled smoke exhaust are the same; the different names are only for descriptive convenience.

[0065] Corresponding to the preheating process of low-oxygen-enriched air and low-calorific-value coal gas are the flow paths of these two gases. Specifically, the flow path of the low-oxygen-enriched air is as follows: the unpreheated low-oxygen-enriched air is first pressurized by the blower 229, then preheated in two stages by the low-temperature air preheater 225 and the high-temperature air preheater 222, and finally injected into the furnace through the air channels of the burners located in the heating section 212 and the soaking section 211 to aid combustion of the low-calorific-value coal gas. The flow path of the low-calorific-value coal gas is as follows: first, low-calorific-value coal gas is prepared by mixing raw coal gas; after mixing, it enters the low-temperature coal gas preheater 224 through valve group 227, then undergoes two stages of preheating by the low-temperature coal gas preheater 224 and the high-temperature coal gas preheater 223, and finally is injected into the furnace through the gas channels of the burners located in the heating section 212 and the soaking section 211 for combustion reaction.

[0066] In summary, the steel rolling heating method for coupled continuous combustion of low-oxygen-enriched air and low-calorific-value gas provided in the embodiments of the present invention has the following beneficial effects:

[0067] 1) Eliminating the gas storage reversal completely solves the process and structural problems of gas release in existing regenerative heating furnace technology, avoiding the waste of a large amount of high-quality gas and serious environmental pollution.

[0068] 2) The elimination of gas regenerative reversal has thoroughly improved the technical problem of poor occupational health environment in existing regenerative heating furnace technology.

[0069] 3) It eliminates the need for supplementary combustion gas consumption in the denitrification system. At the same time, it avoids energy waste caused by the release of large amounts of coal gas, fundamentally reducing CO2 emissions in the steel rolling process. It is a low-carbon combustion technology for low-calorific-value coal gas with significant effects.

[0070] 4) The elimination of the gas thermal storage reversing system significantly reduced the accident rate of the heating furnace and greatly reduced the workload and cost of heating furnace maintenance.

[0071] 5) By adopting a continuous combustion method instead of a discontinuous combustion method, the heating furnace can achieve a more precise intelligent heating process. At the same time, the heating intensity increases and the oxidation rate decreases.

[0072] 6) The use of hot water or saturated steam production equipment to recover the intermediate temperature waste heat from the flue gas has greatly improved the efficiency of waste heat utilization.

[0073] like Figure 2 As shown, this invention provides a steel rolling heating system for continuous combustion of low-oxygen-enriched air and low-calorific-value gas, comprising: a preheating system 220, used to preheat the low-oxygen-enriched air and low-calorific-value gas to a target temperature, wherein the target temperature is 350-450°C, the oxygen content of the low-oxygen-enriched air is 24-30%, and the calorific value of the low-calorific-value gas is 1000-1200 Kcal / m³. 3 The furnace chamber 210 includes a preheating section 213, a heating section 212, and a soaking section 211 arranged sequentially according to the order in which the steel billet passes after entering the furnace. The soaking section 211 and the heating section 212 are respectively provided with combustion devices 214 connected to the preheating system 210. These devices are used to transport low-oxygen-enriched air and low-calorific-value gas preheated to the target temperature into the soaking section 211 and the heating section 212 for continuous combustion to heat the steel billet entering the heating section 212 and the soaking section 211. The preheating section 213 is provided with a flue gas outlet, so that the high-temperature flue gas generated by the combustion of the low-oxygen-enriched air and the low-calorific-value gas flows from the soaking section 211 and the heating section 212 to the preheating section 213, and preheats the steel billet entering the preheating section 213 when it flows to the preheating section 213.

[0074] In some embodiments, in the steel rolling heating system of coupled continuous combustion of low oxygen-enriched air and low calorific value gas, at least two combustion devices 214 are symmetrically arranged in the heat soaking section 211, and at least two combustion devices 214 are symmetrically arranged in the heating section 212.

[0075] In some embodiments, in the steel rolling heating system of coupled continuous combustion of low-oxygen-enriched air and low-calorific-value gas, the preheating system 220 includes: a hot water or saturated steam production device 221, which is connected to the flue gas outlet of the preheating section 213, for supplying medium-temperature flue gas to produce hot water or saturated steam, and cooling the medium-temperature flue gas to a sub-medium-temperature flue gas, wherein the medium-temperature flue gas is the preheating gas that flows from the high-temperature flue gas to the preheating section 213 and preheats the steel billet entering the preheating section 213. The system comprises: a high-temperature air preheater 222, located on the flue gas outlet side of the hot water or saturated steam production unit 221, for supplying low-oxygen-enriched air preheated at low temperature and the secondary medium-temperature flue gas therein, and utilizing the secondary medium-temperature flue gas to preheat the low-oxygen-enriched air to the target temperature; and a high-temperature coal gas preheater 223, located on the flue gas outlet side of the hot water or saturated steam production unit 221, for supplying low-calorific-value coal gas preheated at low temperature and the secondary medium-temperature flue gas. The gas is fed into the preheater, where the low-calorific-value coal gas, which has already been preheated at low temperature, is preheated to the target temperature using the intermediate-temperature flue gas. A low-temperature air preheater 225, located on the flue gas outlet side of the high-temperature air preheater 222, is used to supply unpreheated low-oxygen-enriched air and the intermediate-temperature flue gas flowing out of the high-temperature air preheater 222 and the high-temperature coal gas preheater 223. The low-temperature air preheater 225, located on the flue gas outlet side of the high-temperature air preheater 222, supplies the unpreheated low-oxygen-enriched air and the intermediate-temperature flue gas flowing out of the high-temperature air preheater 222 and the high-temperature coal gas preheater 223. Low-oxygen-enriched air is preheated to 250-300°C at a low temperature; a low-temperature gas preheater 224 is installed on the flue gas outlet side of the high-temperature gas preheater 223, and is used to supply unpreheated low-calorific-value gas and the secondary medium-temperature flue gas flowing out of the high-temperature air preheater 222 and the high-temperature gas preheater 223 to it, and uses the secondary medium-temperature flue gas flowing out of the high-temperature air preheater 222 and the high-temperature gas preheater 223 to preheat the unpreheated low-calorific-value gas to 250-300°C at a low temperature.

[0076] In some embodiments, in the steel rolling heating system of coupled continuous combustion of low-oxygen-enriched air and low-calorific-value coal gas, the preheating system 220 further includes: a flue gas purification device 226, which is disposed on the flue gas outlet side of the high-temperature air preheater 222 and the high-temperature coal gas preheater 223, and the low-temperature air preheater 225 and the low-temperature coal gas preheater 224 are disposed on the flue gas outlet side of the flue gas purification device 226, for supplying the secondary medium-temperature flue gas flowing out of the high-temperature air preheater 222 and the high-temperature coal gas preheater 223 to it, and purifying the secondary medium-temperature flue gas flowing out of the high-temperature air preheater 222 and the high-temperature coal gas preheater 224.

[0077] In summary, the steel rolling heating system with coupled continuous combustion of low-oxygen-enriched air and low-calorific-value gas provided in the embodiments of the present invention has the following beneficial effects:

[0078] 1) Eliminating the gas storage reversal completely solves the process and structural problems of gas release in existing regenerative heating furnace technology, avoiding the waste of a large amount of high-quality gas and serious environmental pollution.

[0079] 2) The elimination of gas regenerative reversal has thoroughly improved the technical problem of poor occupational health environment in existing regenerative heating furnace technology.

[0080] 3) It eliminates the need for supplementary combustion gas consumption in the denitrification system. At the same time, it avoids energy waste caused by the release of large amounts of coal gas, fundamentally reducing CO2 emissions in the steel rolling process. It is a low-carbon combustion technology for low-calorific-value coal gas with significant effects.

[0081] 4) The elimination of the gas thermal storage reversing system significantly reduced the accident rate of the heating furnace and greatly reduced the workload and cost of heating furnace maintenance.

[0082] 5) By adopting a continuous combustion method instead of a discontinuous combustion method, the heating furnace can achieve a more precise intelligent heating process. At the same time, the heating intensity increases and the oxidation rate decreases.

[0083] 6) The use of hot water or saturated steam production equipment to recover the intermediate temperature waste heat from the flue gas has greatly improved the efficiency of waste heat utilization.

[0084] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. It can be applied to various fields suitable for the present invention. Other modifications can be readily made by those skilled in the art. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and examples shown and described herein.

Claims

1. A method for heating steel rolling mills through continuous combustion of low-oxygen-enriched air and low-calorific-value gas, characterized in that, include: Low-oxygen-enriched air and low-calorific-value coal gas are preheated to a target temperature, wherein the target temperature is 350~450℃, the oxygen content of the low-oxygen-enriched air is 24~30%, and the calorific value of the low-calorific-value coal gas is 1000-1200 kcal / m³. 3 ; Low-oxygen-enriched air and low-calorific-value gas, preheated to the target temperature, are delivered to the furnace chamber of the heating furnace for continuous combustion to heat the steel billet entering the furnace chamber. The furnace chamber of the heating furnace includes a preheating section, a heating section and a homogenizing section arranged in the order in which the steel billet passes through after entering the furnace. The flow direction of the low oxygen-enriched air and the high-temperature flue gas generated by the combustion of the low-calorific-value gas is from the homogenizing section and the heating section to the preheating section. The process of supplying preheated, low-oxygen-enriched air and low-calorific-value gas to the furnace chamber for continuous combustion to heat the steel billet entering the furnace chamber includes: Preheated air with low oxygen content and low calorific value gas to the target temperature are transported to the homogenization section and the heating section for continuous combustion. The low-oxygen-enriched air and the high-temperature flue gas generated by the combustion of low-calorific-value coal gas, which are preheated to the target temperature, flow to the preheating section to preheat the steel billet entering the preheating section. As the steel billet sequentially enters the heating section and the soaking section from the preheating section, the steel billet entering the heating section and the soaking section is heated sequentially by the continuous combustion of low oxygen-enriched air and low calorific value gas preheated to the target temperature in the heating section and the soaking section. The process of preheating low-oxygen-enriched air and low-calorific-value gas to the target temperature includes: The low-oxygen-enriched air and the low-calorific-value gas are preheated to the target temperature using the medium-temperature flue gas flowing out of the furnace chamber of the heating furnace. The medium-temperature flue gas is formed by the high-temperature flue gas flowing to the preheating section and preheating the steel billet entering the preheating section before cooling it down. The furnace chamber of the heating furnace is provided with a hot water or saturated steam production device, a high-temperature air preheater, a high-temperature gas preheater, a low-temperature air preheater, and a low-temperature gas preheater on the flue gas outlet side. The high-temperature air preheater and the high-temperature gas preheater are arranged side by side on the flue gas outlet side of the hot water or saturated steam production device, the low-temperature air preheater is arranged on the flue gas outlet side of the high-temperature air preheater, and the low-temperature gas preheater is arranged on the flue gas outlet side of the high-temperature gas preheater. The step of preheating the low-oxygen-enrichment air and the low-calorific-value coal gas to the target temperature using the medium-temperature flue gas includes: The intermediate-temperature flue gas is transported to a hot water or saturated steam production device to produce hot water or saturated steam, thereby cooling the intermediate-temperature flue gas into sub-intermediate-temperature flue gas. Low-oxygen-enriched air and low-calorific-value coal gas that have been preheated at low temperature are respectively transported to the high-temperature air preheater and the high-temperature coal gas preheater. The intermediate-temperature flue gas is transported to the high-temperature air preheater and the high-temperature coal gas preheater. The intermediate-temperature flue gas is used to preheat the low-oxygen-enriched air and low-calorific-value coal gas that have been preheated at low temperature to the target temperature. Unpreheated low-oxygen-enriched air and low-calorific-value coal gas are respectively fed to the low-temperature air preheater and the low-temperature coal gas preheater. The secondary medium-temperature flue gas flowing out of the high-temperature air preheater and the high-temperature coal gas preheater is fed to the low-temperature air preheater and the low-temperature coal gas preheater. The secondary medium-temperature flue gas flowing out of the high-temperature air preheater and the high-temperature coal gas preheater are used to preheat the unpreheated low-oxygen-enriched air and low-calorific-value coal gas to 250~300℃. The high-temperature air preheater and the high-temperature gas preheater are equipped with flue gas purification devices on their flue gas outlet sides, and the low-temperature air preheater and the low-temperature gas preheater are located on the flue gas outlet side of the flue gas purification devices; the method further includes: The secondary and intermediate temperature flue gas flowing out of the high-temperature air preheater and the high-temperature gas preheater is transported to the flue gas purification device for purification.

2. The steel rolling heating method for continuous combustion of low-oxygen-enriched air and low-calorific-value gas as described in claim 1, characterized in that, The low-calorific-value gas is a mixture of blast furnace gas and converter gas, or a mixture of blast furnace gas and natural gas, or a mixture of blast furnace gas and coke oven gas.

3. A steel rolling heating system for continuous combustion of low-oxygen-enriched air and low-calorific-value gas, characterized in that, include: A preheating system is used to preheat low-oxygen-enriched air and low-calorific-value coal gas to a target temperature, wherein the target temperature is 350~450℃, the oxygen content of the low-oxygen-enriched air is 24~30%, and the calorific value of the low-calorific-value coal gas is 1000-1200 kcal / m³. 3 ; The furnace chamber of the heating furnace includes a preheating section, a heating section, and a soaking section arranged sequentially according to the order in which the steel billet passes after entering the furnace. The soaking section and the heating section are respectively equipped with combustion devices connected to the preheating system, which are used to transport low-oxygen-enriched air and low-calorific-value gas preheated to the target temperature into the soaking section and the heating section for continuous combustion to heat the steel billet entering the heating section and the soaking section. The preheating section is provided with a flue gas outlet, so that the high-temperature flue gas generated by the combustion of the low-oxygen-enriched air and the low-calorific-value gas flows from the soaking section and the heating section to the preheating section, and preheats the steel billet entering the preheating section when it flows to the preheating section. The preheating system includes: A hot water or saturated steam production device is connected to the flue gas outlet of the preheating section for supplying medium-temperature flue gas to produce hot water or saturated steam and cooling the medium-temperature flue gas to a sub-medium-temperature flue gas. The medium-temperature flue gas is formed by the high-temperature flue gas flowing to the preheating section and preheating the steel billet entering the preheating section before cooling it down. A high-temperature air preheater is installed on the flue gas outlet side of the hot water or saturated steam production device. It is used to supply low-oxygen-enriched air that has been preheated at low temperature and the secondary medium-temperature flue gas to it, and to use the secondary medium-temperature flue gas to preheat the low-oxygen-enriched air that has been preheated at low temperature to the target temperature. A high-temperature gas preheater is installed on the flue gas outlet side of the hot water or saturated steam production device. It is used to supply low-calorific-value gas that has been preheated at low temperature and the secondary medium-temperature flue gas to it, and to use the secondary medium-temperature flue gas to preheat the low-calorific-value gas that has been preheated at low temperature to the target temperature. A low-temperature air preheater is installed on the flue gas outlet side of the high-temperature air preheater. It is used to supply unpreheated low-oxygen-enriched air and secondary medium-temperature flue gas flowing out of the high-temperature air preheater and the high-temperature gas preheater to it. The secondary medium-temperature flue gas flowing out of the high-temperature air preheater and the high-temperature gas preheater is used to preheat the unpreheated low-oxygen-enriched air to 250~300°C. A low-temperature gas preheater is installed on the flue gas outlet side of the high-temperature gas preheater. It is used to supply unpreheated low-calorific-value gas and the secondary medium-temperature flue gas flowing out of the high-temperature air preheater and the high-temperature gas preheater to it. The secondary medium-temperature flue gas flowing out of the high-temperature air preheater and the high-temperature gas preheater is used to preheat the unpreheated low-calorific-value gas to 250~300°C. The heat spreader section is symmetrically provided with at least two of the combustion devices, and the heating section is symmetrically provided with at least two of the combustion devices.

4. The steel rolling heating system for continuous combustion of low-oxygen-enriched air and low-calorific-value gas as described in claim 3, characterized in that, The preheating system also includes: A flue gas purification device is installed on the flue gas outlet side of the high-temperature air preheater and the high-temperature gas preheater. The low-temperature air preheater and the low-temperature gas preheater are installed on the flue gas outlet side of the flue gas purification device. The device is used to supply the secondary and intermediate temperature flue gas flowing out of the high-temperature air preheater and the high-temperature gas preheater to the device and to purify the secondary and intermediate temperature flue gas flowing out of the high-temperature air preheater and the high-temperature gas preheater.

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