Abstract: Blast furnace gas is released in large quantities due to its low heating value and low combustion efficiency. A Cu-based adsorbent pressure swing adsorption process is used to purify CO in blast furnace gas to increase its heating value and combustion efficiency. It is used in downstream production for energy saving and consumption reduction. Protecting the environment is of great significance.
Keywords: blast furnace gas, copper sorbent, calorific value
China is a large steel producer, and pig iron output has been increasing year by year in recent years. At present, the total energy consumption of the iron and steel industry accounts for about 15% of the total industrial energy consumption in the country, while the energy efficiency in the production process of steel companies is only about 30%. In iron and steel enterprises, blast furnace ironmaking is the most energy-intensive link. The energy conservation of the steel industry mainly includes two aspects: reducing waste and increasing recycling. Among them, vigorously recovering secondary energy (such as by-product gas) generated in the production process is a very important way. By-product gas resources in steel production include blast furnace gas, coke oven gas and converter gas. Among them, blast furnace gas emissions account for about 64%, coke oven gas accounts for about 29%, and converter gas accounts for about 7%. Therefore, the effective use of blast furnace gas is the top priority of energy saving and consumption reduction in steel plants.
Blast furnace gas is a by-product of the blast furnace ironmaking process. It is a colorless, odorless, and toxic low-calorific gas fuel. The main components are CO, CO2, N2, H2O, and a small amount of H2. The content of each component is closely related to the fuel used in the blast furnace, the pig iron type, and the smelting process. The common composition is shown in Table 1.
Table 1 Composition of common blast furnace gas
The CO content with the most secondary use value is only 25-30%, and the inert components CO2 and N2 account for about 70%, which makes the calorific value of the blast furnace gas very low, generally only about 730-800 × 4.18 KJ / Nm3 Only when the calorific value of the fuel reaches about 2200 × 4.18KJ / Nm3 can the theoretical combustion temperature requirements of industrial furnaces be met.
At present, the utilization of blast furnace gas is inadequate. Most metallurgical plants are in short supply of high calorific value gas, and there is a surplus of blast furnace gas. There are different degrees of blast furnace gas release, which cannot achieve the effective use of gas 111. Many iron and steel joint ventures are releasing blast furnace gas on the one hand, and on the other hand they are buying heavy oil, natural gas or burning their own tar as energy supplements. The blast furnace's own hot blast stove will use 40% to 50% of the blast furnace gas. If most of the rest is released into the atmosphere, it will cause environmental pollution and waste of energy. The "China Energy Conservation Technology Outline" issued by the State Planning Commission, the Economic and Trade Commission and the Science and Technology Commission requires that the blast furnace gas emission loss rate of key metallurgical enterprises should be less than 4%.
At present, in the production of metallurgical joint ventures, blast furnace gas can be used in hot blast stoves, coking, heating furnaces and power generation.
1) Blast furnace gas is used in steel rolling heating furnaces and adopts regenerative combustion technology. Using high temperature air combustion technology, pre-heat both blast furnace gas and combustion air to above 1000 ℃, so that the theoretical combustion temperature of a single blast furnace gas reaches above 2200 ℃, and the thermal efficiency is about 30% higher than that of a conventional heating furnace. Regenerative combustion furnaces are difficult to control gas supply, stable furnace pressure and stable combustion, long reconstruction time and high maintenance costs.
2) Blast furnace gas is mixed with high calorific value gas fuel to form a sub-high calorific fuel that meets the requirements of the heating furnace. It can be mixed with coke oven gas, natural gas, liquefied petroleum gas, etc., and used as fuel for furnaces such as soaking furnaces, heating furnaces, and heat treatment furnaces. It can also be used for ignition of sintering machines, heating of hot-rolled steel ingots, and preheating of ladle.
3) Blast furnace gas is used to burn boilers, which can be used to generate electricity at the same time as factory steam. Blast furnace gas and steam combined cycle power generation (CCPP for short) has high efficiency and low cost, but huge construction investment; it is not economical to supply to other enterprises.
4) Separately preheat the blast furnace gas to increase the temperature of the steel rolling furnace.
Pioneer of Peking University designed and built a PSA blast furnace gas enrichment CO device for Valin Henggang in 2012. It adopts pressure swing adsorption technology and uses Cu-based adsorbent to separate and purify CO from blast furnace gas. The PSA method has the advantages of less investment, large operating flexibility, high degree of automation, and simple operation. The Cu-based adsorbent has a larger separation coefficient for CO and N2 than the 5A molecular sieve used in conventional PSA, which is especially suitable for it. CO is purified from blast furnace gas with high nitrogen content.
1 Purification of CO in blast furnace gas by pressure swing adsorption method using Cu-based adsorbent
In this paper, the Henggang Baida Pioneer Energy Technology Co., Ltd. blast furnace gas PSA purification CO plant in Hunan Province, which is put into production, is used as an example to introduce the application of CO2 separation using Peking Pioneer PSA technology. The designed yield of the device is 92%. The concentration of CO product gas can be adjusted within the range of 60% to 70% according to user needs. The product gas is used as fuel for steel pipe processing. The design flow chart, raw gas composition, and product gas requirements are shown in Figure 1, Table 2, and Table 3.
Figure 1 Process flow diagram
Table 2 Feed gas composition
Table 3 Product gas requirements
2 Process flow
Because the blast furnace gas contains trace impurities such as COS and O2, and the content is unstable, a pretreatment procedure is designed in this process. This process adopts desulfurization and deoxygenation processes. The desulfurization tower and deoxygenation tower are filled with Peking Pioneer Technology Co., Ltd.'s proprietary desulfurizer and deoxidizer, so that the total sulfur in the blast furnace gas is removed to the pressure swing adsorption process. Below 1 ppm, O2 is removed to below 5 ppm.
The desulfurization process uses dry desulfurization, which mainly includes three steps: room temperature hydrolysis, crude desulfurization, and fine desulfurization. In the hydrolysis step, most of the COS is hydrolyzed to H2S with a hydrolysis rate of greater than 95%; after the hydrolyzed gas undergoes crude desulfurization, most of the H2S is adsorbed by the desulfurizing agent; the remaining COS and H2S are absorbed by fine desulfurization, and the total Sulfur removal is below 1 ppm. The deoxidation process uses PU-5 deoxidizer independently developed by Pioneer of Peking University. Under the CO atmosphere, it catalyzes the reaction of trace O2 and CO to remove O2 to less than 5ppm.
PSA-CO process adopts pressure swing adsorption separation process. The pre-treated clean gas is separated and purified in the PSA-CO process through adsorption, pressure equalization and pressure reduction, discharge, vacuum, pressure equalization, and final charging and pressure cycling. CO. CO is precipitated as product gas at atmospheric pressure, compressed by a compressor to the user's required pressure, and sent to the user's place of use. The PSA-CO process uses a high-efficiency CO adsorbent developed by Peking University Pioneer. Without using a replacement step, it not only meets the high purity requirements of the CO product, but also saves one-time investment and operating costs. The process is relatively simplified and the operation changes. Be simple and easy to control.
3 Analysis of actual operating results of the device
The blast furnace gas purification CO device has been operating stably after a successful one-time start-up on June 8, 2013, and can also meet the requirements for use under various operating conditions when the blast furnace production fluctuates greatly. The average product gas specifications (gas chromatography external standard method) measured during actual operation for 72 hours are as follows.
Table 4 Product gas components
In actual operation, the COS concentration in the blast furnace gas often changes and fluctuates between 50 and 120 ppm. The pretreatment process can completely remove COS through proper temperature adjustment.
The design value of the CO content in the blast furnace gas is 24%, but it is only 18 to 22% during actual operation. Within this concentration range, the CO content in the CO product gas can still meet the design requirements. When the CO concentration in the feed gas is> 20%, the CO concentration in the product gas is> 72%.
The average blast furnace gas consumption is 60,000 Nm3 / h, and the CO product gas volume is 18,000 Nm3 / h. The yield is about 93%. The purity of the product can be adjusted within the range of 60% to 70% according to needs. Significant energy saving effect. Calculated according to the calorific value of product gas and natural gas, CO product gas can replace natural gas 4537m3 per hour, and the annual replacement volume reaches 3974 * 104m3, which is equivalent to about 1/3 of Henggang's original natural gas consumption, which greatly eases Henggang's use of gas. A tense situation.
Blast furnace gas is rich in CO gas and has a high value for use. Using the Pioneer Cu-based adsorbent PSA process to separate and purify the CO gas in the blast furnace gas, the CO component content in the blast furnace gas was purified from 22% (calorific value 731Kcal / Nm3) to 70% (calorific value 2200Kcal / Nm3), As fuel gas used in steel pipe processing, it is of great significance in terms of energy saving and consumption reduction. In addition, using this technology can also increase the CO in blast furnace gas to more than 98.5%, which can be used in chemical production, synthesis of ethylene glycol, dimethyl carbonate, acetic acid, methanol, TDI, DMF, etc., which not only achieved The integration of resources in the steel and chemical industries has good economic benefits. It also helps reduce the overall primary energy use of steel and chemical companies, thereby reducing carbon dioxide emissions, promoting industrial coupling, and promoting the industry to achieve green, low-carbon, sustainable development.