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.

2 礦熱爐尾氣的燃燒特性和利用難點

The combustion characteristics and utilization difficulties of exhaust gas from a submerged arc furnace

FOF的熱值通常只有天然氣熱值的1/3左右，也就是說相比于同級輸出功率的天然氣機型，F(xiàn)OF發(fā)電機組的進氣量需要增大3倍以上。FOF的抗爆性與天然氣也有顯著區(qū)別，其甲烷指數(shù)(Methane Number，簡稱MN)只有天然氣的大約60%左右，這意味著這種氣體在內(nèi)燃機氣缸里面更容易發(fā)生爆震。所以，燃?xì)獍l(fā)電機組需要通過傳感器監(jiān)測爆震的發(fā)生以調(diào)整機組的運行狀態(tài)。另一方面，F(xiàn)OF燃燒時的層流火焰速度(Laminar Flame Speed，簡稱LFS)卻比天然氣快許多，這和氣體里面氫氣的含量比例有關(guān)。層流火焰速度是在層流前沿發(fā)生氧化反應(yīng)的速度， 即未燃燒的混合氣與火焰前沿之間的相對速度。根據(jù)麻省理工學(xué)院的研究資料，在當(dāng)量比(Equivalence Ratio)為2時，5% H2和95% CO組成的混合氣的LFS約為50cm/s，而 50% H2和50% CO組成的混合氣的LFS可到160cm/s。鑒于FOF特殊的燃燒特性，燃?xì)鈨?nèi)燃機的進氣系統(tǒng)和控制參數(shù)都需要特殊設(shè)計以適應(yīng)其特性，同時還必須滿足NOx的排放要求。

The calorific value of FOF 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 generator sets 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. 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.

山東中拓的 DIA.NE XT4系統(tǒng)在氣體質(zhì)量波動時自動調(diào)整設(shè)置，因此能夠適應(yīng)復(fù)雜的運行情況。同時，山東中拓的LEANOX稀薄燃燒控制技術(shù)能夠?qū)崟r控制氮氧化物NOx的排放，確保始終滿足嚴(yán)苛的環(huán)保要求，使機組排氣出口NOx達到250-500mg/Nm3(@5% O2)，并且無需SCR等復(fù)雜的尾氣后處理裝置。新的山東中拓資產(chǎn)管理系統(tǒng)myPlant則能實時監(jiān)測、控制和預(yù)測機組的運行狀態(tài)，并能提供前瞻性的維護保養(yǎng)建議。

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.

圖2 H2和CO混合氣的層流火焰速度（來源：MIT）

Figure 2 laminar flame velocity of H2 and CO mixture (source: MIT)

3 燃?xì)鈨?nèi)燃機對氣體的雜質(zhì)含量要求

3. Requirements for impurity content of gas in gas internal combustion engines

尾氣的成分和氣量與爐子的運行參數(shù)有關(guān)，并受到原料質(zhì)量、爐子控制和運行狀態(tài)等因素的影響，所以通常會連續(xù)變化。采用氣柜來減少氣體熱值和壓力的波動，對于燃?xì)鈨?nèi)燃機發(fā)電非常重要。在爐子供氣中斷時，氣柜還可以起到緩沖的作用。

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.

進入內(nèi)燃機前的FOF需要進行預(yù)處理，以滿足氣體質(zhì)量要求。通常需要去除粉塵，以及多余的水分，還有焦油、硫及其他有害雜質(zhì)等。硫、氨等成分的含量要求與燃?xì)獾臒嶂迪嚓P(guān)，須根據(jù)實際熱值確定上限值。下表是山東中拓燃?xì)鈨?nèi)燃機對氣體的一般質(zhì)量要求。

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.

燃?xì)赓|(zhì)量范圍或上限值

Gas quality range or upper limit value

壓力波動(kPa/s)1

Pressure fluctuation (kPa/s) 1

熱值波動(%/min)4

Calorific value fluctuation (%/min) 4

3μm以上顆粒過濾效率(客戶提供運行過濾器)>99.99%

three μ Particle filtration efficiency above m (customer provided running filter)>99.99%

溫度(°C)10~40

Temperature (° C) 10~40

相對濕度<80%

Relative humidity<80%