Natural gas, biogas, landfill gas, and coal mine gas are common gases that can be applied to gas internal combustion engines. In addition, there are some industrial waste gases that contain combustible components, such as hydrogen and carbon monoxide. The tail gas of the submerged arc furnace is one of the industrial waste gases that can enter the gas internal combustion engine for power generation. Although this type of exhaust gas has many impurities and low calorific value, after purification treatment, it can enter the gas internal combustion engine for power generation, thereby realizing the transformation of waste into treasure, energy conservation and emission reduction, and creating considerable economic benefits.
Mineral arc furnace, also known as electric arc furnace or resistance furnace. It is mainly used for reducing smelting ores, carbon reducing agents, solvents and other raw materials, and mainly produces ferroalloys such as ferrosilicon, ferromanganese, ferrochromium, ferrotungsten, and silicomanganese alloys. Mineral heat furnaces are mainly divided into two types: semi enclosed and enclosed furnaces. The exhaust gas generated by enclosed furnaces contains more combustible components and can be used for gas internal combustion engine power generation.
Figure 1 Production and Utilization Process of Tail Gas from a Mine Heating Furnace
在矿热炉生产铁合金的过程中产生的尾气(Furnace off gas，简称FOF)主要成分为CO，以及少量的 H2、 CO2等。其中一氧化碳(CO)气体是由于还原剂中存在碳而形成的，如果还原剂中含有挥发性碳氢化合物，则会形成氢气(H2)。过去，矿热炉尾气通常是直接燃烧后排放，而现在则可以通过高效的燃气内燃机发电，同时利用高温烟气的热能，使能源得到高效充分的利用。
The exhaust gas (FOF) generated during the production of ferroalloys in a submerged arc furnace is mainly composed of CO, as well as a small amount of H2, CO2, etc. Carbon monoxide (CO) gas is formed due to the presence of carbon in the reducing agent. If the reducing agent contains volatile hydrocarbons, hydrogen gas (H2) will be formed. In the past, the exhaust gas from submerged arc furnaces was usually discharged after direct combustion. However, now it can be generated through efficient gas internal combustion engines, while utilizing the heat energy of high-temperature flue gas to efficiently and fully utilize energy.
The calorific value of FOF power generation units is usually only about one-third of that of natural gas, which means that compared to natural gas models with the same level of output power, the intake volume of FOF power generation units needs to be increased by more than three times. The anti knock performance of FOF is also significantly different from that of natural gas, with its Methane Number (MN) only about 60% of that of natural gas, which means that this gas is more prone to detonation in internal combustion engine cylinders. Therefore, gas generator units need to monitor the occurrence of detonation through sensors to adjust the operating status of the unit.
另一方面，FOF燃烧时的层流火焰速度(Laminar Flame Speed，简称LFS)却比天然气快许多，这和气体里面氢气的含量比例有关。层流火焰速度是在层流前沿发生氧化反应的速度， 即未燃烧的混合气与火焰前沿之间的相对速度。根据麻省理工学院的研究资料，在当量比(Equivalence Ratio)为2时，5% H2和95% CO组成的混合气的LFS约为50cm/s，而 50% H2和50% CO组成的混合气的LFS可到160cm/s。鉴于FOF特殊的燃烧特性，燃气内燃机的进气系统和控制参数都需要特殊设计以适应其特性，同时还必须满足NOx的排放要求。
On the other hand, the laminar flame speed (LFS) during FOF combustion is much faster than natural gas, which is related to the proportion of hydrogen content in the gas. The laminar flame velocity is the rate at which oxidation reactions occur at the front of the laminar flow, that is, the relative velocity between the unburned mixture and the flame front. According to research data from the Massachusetts Institute of Technology, when the equivalence ratio is 2, the LFS of a mixture of 5% H2 and 95% CO is about 50cm/s, while the LFS of a mixture of 50% H2 and 50% CO can reach 160cm/s. Given the unique combustion characteristics of FOF, the intake system and control parameters of gas internal combustion engines require special design to adapt to their characteristics, while also meeting the NOx emission requirements.
颜巴赫的 DIA.NE XT4系统在气体质量波动时自动调整设置，因此能够适应复杂的运行情况。同时，颜巴赫的LEANOX稀薄燃烧控制技术能够实时控制氮氧化物NOx的排放，确保始终满足严苛的环保要求，使机组排气出口NOx达到250-500mg/Nm3(@5% O2)，并且无需SCR等复杂的尾气后处理装置。新的颜巴赫资产管理系统myPlant则能实时监测、控制和预测机组的运行状态，并能提供前瞻性的维护保养建议。
Yanbach's advanced DIA. NE XT4 system automatically adjusts settings when gas quality fluctuates, thus being able to adapt to complex operating conditions. At the same time, Yanbach's LEANOX lean combustion control technology can control the emission of nitrogen oxide NOx in real-time, ensuring that strict environmental requirements are always met, so that the NOx at the exhaust outlet of the unit can reach 250-500mg/Nm3 (@ 5% O2), and there is no need for complex tail gas post-treatment devices such as SCR. The new Yanbach asset management system myPlant can monitor, control, and predict the operating status of the unit in real-time, and provide forward-looking maintenance recommendations.
Requirements for impurity content of gas in gas internal combustion engines
The composition and gas volume of exhaust gas are related to the operating parameters of the furnace, and are influenced by factors such as raw material quality, furnace control, and operating status, so they usually change continuously. The use of gas cabinets to reduce fluctuations in gas calorific value and pressure is very important for gas internal combustion engine power generation. When the gas supply to the furnace is interrupted, the gas holder can also serve as a buffer.
The FOF before entering the internal combustion engine requires pre-treatment to meet the gas quality requirements. Usually, it is necessary to remove dust, excess water, tar, sulfur, and other harmful impurities. The content requirements of components such as sulfur and ammonia are related to the calorific value of the gas, and the upper limit value must be determined based on the actual calorific value. The following table shows the general quality requirements for gases in Yanbach gas internal combustion engines.
South African Ilmenite Smelter Mine Furnace Tail Gas Power Generation Project
南非大的一家钛铁矿冶炼工厂于2012年采用了8台颜巴赫J620燃气发电机组，每台功率1,698 kW，总容量13.6 MW。所发出的电力并入公司11 kV内网，用于满足工厂部分电能需求。
A large titanium iron ore smelting plant in South Africa adopted 8 Yanbach J620 gas generator units in 2012, each with a power of 1698 kW and a total capacity of 13.6 MW. The electricity generated is integrated into the company's 11 kV internal network to meet some of the power needs of the factory.
工厂内有两个封闭的直流电弧炉，产生尾气主要成分为73% CO, 14.5% H2，以及少量CO2等。据测算，该项目平均每年大约可以减少84,432 吨二氧化碳排放，是联合国清洁发展机制CDM注册项目。
There are two enclosed DC arc furnaces in the factory, which produce tail gas mainly composed of 73% CO, 14.5% H2, and a small amount of CO2. According to calculations, the project can reduce carbon dioxide emissions by approximately 84432 tons per year on average, making it a registered CDM project under the United Nations Clean Development Mechanism.
Norwegian manganese iron alloy submerged arc furnace tail gas power generation project
北欧大的锰铁合金生产商采用了1台颜巴赫J620燃气发电机组用于矿热炉尾气发电 ，输出功率 1.5MW。尾气的主要成分为65% CO, 5% H2, 8% CO2等，低位热值(LHV)大约2.8 kWh/Nm3。项目于2020年调试完成并投入商业运行。
Nordic manganese iron alloy manufacturers have adopted one Yanbach J620 gas generator unit for generating tail gas from submerged arc furnaces, with an output power of 1.5MW. The main components of exhaust gas are 65% CO, 5% H2, 8% CO2, etc., with a low calorific value (LHV) of approximately 2.8 kWh/Nm3. The project was commissioned and completed in 2020 and put into commercial operation.
By recycling the exhaust gas from the ore furnace for the combined heat and power supply system (CHP), the factory's demand for electricity from the power grid is reduced, saving electricity costs. The high-temperature flue gas generated by the system is used to dry the ore before smelting. The goal of the factory is to increase its energy efficiency by 40% through the use of CHP. At the same time, the project has also received strong support from the Norwegian government due to its outstanding contributions in environmental protection and energy conservation and emission reduction.
The power generation application of the tail gas of the submerged arc furnace fully utilizes the exhaust gas, converting it into electrical and thermal energy, and is an example of energy conservation, emission reduction, and circular economy in the smelting industry. By utilizing exhaust gas to turn waste into treasure, we can improve environmental emissions while creating new value and saving operating costs for enterprises. Yan Bach has rich experience in this field. His generator set products have high single unit power, high power generation efficiency, short debugging cycle, and good reliability, which can effectively help users achieve considerable profits and significant carbon reduction effects. Against the backdrop of China's "dual carbon" strategic goal, with the continuous improvement of environmental protection requirements for the metallurgical industry, the efficient utilization of tail gas from submerged arc furnaces will have broad development prospects.
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