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Manufactured Gas refer to the combustible gas produced from solid or liquid combustibles such as coal and petroleum through thermal processing methods such as dry distillation, gasification, or cracking. Manufactured gas mainly includes: Coal gasification gas, Coal carbonization gas, and Metallurgical by-product gas, etc.
1. Coal Gasification Gas, refer to the combustible gas produced by the chemical reaction of coal or coke with gasifying agents (such as air, oxygen, water vapor) at high temperatures. The main components include hydrogen (H₂), carbon monoxide (CO), and a small amount of methane (CH₄). Typical gasification gases include Producer gas, Water gas, and Semi-water gas, etc.
Gasification Gas is a kind combustible gas which is produced by crushing, pressure and pyrolysis of fuel coal. It is a combustion mode of clean coal utilization technology. The calorific value of coal gas is lower than that of natural gas, but its preparation is convenient. It can be produced by own equipment without restriction of transportation pipeline. At present, Gasification gas is an irreplaceable flammable gas in the utilization of clean energy. Because of its many advantages, coal gas has been widely used in industrial and mining enterprises, and can be used for power generation and domestic gas.
Coal gasification technology is one of the main ways to produce syngas products. Solid coal is converted into gaseous syngas through gasification process, meantime, by-products such as steam and ash are produced. In coal gasification, there must be three conditions: gasifier, gasifying agent and heat supply. Coal gasification technology can be divided into three categories: fixed bed gasification, circulating fluidized bed gasification and entrained-flow gasification technology. All kinds of gasification technology have their own advantages and disadvantages, and have certain requirements for the quality of raw coal. The advanced technology and maturity degree of technology are also different.
The composition and content of gasification gas vary depending on the gasification agent used.
1.1 Producer Gas, refers to a combustible gas produced by high-temperature gasification of coal or coke with gasifying agents (air and water vapor) in a gasifier. The Lower heating value (LHV): about 900 - 1600 kcal/Nm³, commonly used as industrial heating fuel, can be directly used for power generation. Including: Air producer gas and Mixed gas.
■ Air Producer Gas, refers to a gas fuel produced intermittently (while maintaining furnace temperature) by using air (mainly oxygen) as a gasifying agent and passing it through a high-temperature coal or coke layer for gasification reactions. Due to the large amount of nitrogen in the air, the proportion of non combustible components in the generated gas is high and the calorific value is low. The main combustible components are CO (33% - 37%), CH₄ (< 1%), and H₂ with little or no content. The non combustible components are N₂ (64% - 66%) and CO₂ (0.5% - 1.5%). The Lower heating value (LHV) is about 900 - 1200 kcal/Nm³, and it is currently less commonly used.
■ Mixed Producer Gas, refers to a gas fuel produced continuously through gasification reaction with coal or coke under high temperature conditions, using a mixture of air and water vapor as a gasifying agent. The hydrogen content has increased, but it is still diluted by nitrogen gas, with a calorific value between air gas and water gas. Suitable for various industrial furnaces and can also be used as fuel for power generation.
The main components of Mixed Producer gas (air+steam gasification) after desulfurization treatment are CO (20% - 25%), H₂ (10% - 15%), CH₄ (0.3% - 1%), CmHn (0.7% - 2%), CO₂ (8% - 12%), N₂ (50% - 55%), O₂ (0.1% - 0.5%). The Lower heating value (LHV) range: 5.0 - 6.7 MJ/Nm³ (1200 - 1600 kcal/Nm³), It belongs to low-heating value industrial fuel gas.
1.2 Water Gas, also known as Coal to syngas, refers to a gas fuel produced by the gasification reaction of hot coal with water vapor as a gasifying agent at high temperatures. The main components are CO and H₂, with high calorific value but high production cost. Water gas is the raw material gas for producing synthetic fuels, which can be used to produce synthetic ammonia, hydrogen, and synthetic fuels. It can be directly used as a fuel for power generation.
The main components of Water gas (steam+coke gasification) are: CO (37% - 40%), H₂ (40 - 42%), CH₄ (0.5% - 1%), CO₂ (5% - 8%), N₂ (≤ 1%). The LHV range: 10 - 11.3 MJ/Nm³. belonging to high calorific value chemical feed gas.
1.3 Semi Water Gas, refers to a combustible gas produced by alternately blowing air and a suitable amount of water vapor into a gas generator using coal or coke as fuel. Combining the characteristics of air gas and water gas, it is a commonly used raw material gas in industrial ammonia synthesis and can be directly used as fuel for power generation.
The main components of Semi-water gas (air and steam alternately blown into the gasifier for gasification) are CO (18% - 20%), H₂ (50 - 55%), CH₄ and trace hydrocarbons (0.5% - 1%), N₂ (22% - 23%), CO₂ (5% - 8%), O₂ (< 0.5%). The LHV range: 9.8 - 10.5 MJ/Nm³, belonging to the feed gas specially designed for ammonia synthesis.
2. Coal Carbonization Gas, refers to a combustible mixture gas produced by heating and decomposing coal under isolated air conditions. Its primary constituents encompass hydrogen (H₂), methane (CH₄), and carbon monoxide (CO). Mainly including Coke oven gas, Semi coke gas, and Retort gas.
2.1 Coke Oven Gas (COG), namely High-temperature carbonization gas (900-1100℃), refers to the by-product combustible gas produced in the process of high temperature (about 1000℃) dry distillation of coal in the coking industry. It belongs to a type of metallurgical gas. It is the main fuel for industry and civilian use.
Coke oven gas is a mixture, Its main components are H₂ (55% - 60%) and CH₄ (23% - 27%), as well as small amounts of CO (5% - 8%), CmHn (2% - 4%), CO₂ (1.5% - 3%), O₂ (0.3% - 0.8%), and N₂ (3% -7%). Among them, H₂, CH₄, CO, and CmHn are combustible components. The LHV range: 17 - 18.25 MJ/Nm³ (4063 - 4362 kcal/Nm³). It belongs to medium to high-heating value gas fuel.
2.2 Retort Gas, namely Medium temperature carbonization gas (700-900℃), It refers to the combustible gas produced by the pyrolysis of coal, oil shale, wood or other carbon containing substances under isolated air conditions, heated by a dry distillation furnace (around 850℃). This process often uses continuous upright carbonization furnaces (such as Wood furnaces), which are widely used in fields such as coal upgrading, charcoal production, and biomass resource utilization.
The composition of Retort gas varies depending on the type of raw materials, carbonization temperature, and process conditions. The typical components of continuous upright carbonization furnace gas are CH₄ (56.0%), CO (18.0%), H₂ (17.0%), a small amount of CO₂ (1.7%), N₂ (5.0%), and ethylene(C₂H₄), etc. The LHV: 16.3 MJ/Nm³ (3900 kcal/Nm³), belonging to medium-heating value gas fuel.
2.3. Semi Coke Gas, namely Low-Temperature gas (500-600℃), refers to the by-product combustible gas produced by dry distillation of coal in a 600 ℃ coking furnace to produce semi coke. It can be used as a fuel for power generation.
The main components of Semi coke gas are H₂ (12% - 28%), CH₄ (8.8% - 17%), CO (8% - 12%), CmHn (1% - 3%), N₂ (45% - 50%), CO₂ (2% - 6%),O₂ (0.3% - 0.8%), and H₂S (< 0.5%). The Lower heating value (LHV) range: 6.73 - 8.43 MJ/Nm³ (1609 - 2017 kcal/Nm³), belonging to low-heating value gas fuel.
3. Metallurgical By-product Gas, refers to a combustible mixture of gases containing carbon monoxide produced during the steel smelting process. Including the overlapping category of coke oven gas. It also includes Blast furnace gas, Linz-donawitz gas, and Electric furnace gas.
3.1 Linz-Donawitz Gas (LDG), refers to the combustible gas produced by the action of carbon and oxygen in molten iron during the oxygen-blown converter steelmaking process. LDG contains no sulfur and very little hydrogen, making it an ideal fuel and chemical raw material. The main components of LDG are CO (60% - 80%), CO₂ (15% - 20%), as well as N₂, H₂, and trace amounts of O₂. The LHV around 6200 kJ/Nm³. Belonging to low-heating value gas fuels.
3.2 Blast Furnace Gas (BFG), refers to the combustible gas produced as a byproduct during the ironmaking process of a blast furnace. But the produced gas has a lower calorific value, which increases the difficulty of utilization. If coke oven gas is mixed, the calorific value will be increased. The components of BFG are CO (23% - 30%), H₂ (2% - 4%), CO₂ (12% -15%), N₂ (51 - 56%), CmHn (0.2% - 0.5%), and a small amount of sulfur dioxide. The LHV is only around 3500 kJ/Nm³. Belonging to low-heating value gas fuels.
Gas requirement of Manufactured gas ：
● Gas calorific value ≥ 4.0 MJ/Nm³(Non pressurized sets); Gas temperature ≤ 40℃.
● Gas pressure 2.5-10 kPa; Pressure change rate ≤ 1 kPa/min.
● Hydrogen content (H₂ Volume) ≤ 60% (Non pressurized sets); Hydrogen content (H₂ Volume) ≤ 20% (Pressurized sets);
● Oxygen content (In hydrogen containing gas) ≤ 1%.
● Moisture content ≤ 40 g/Nm³，no free water.
● Impurity content ≤ 30 mg/Nm³; Impurity size ≤ 5 μm.
● Tar content ≤ 50 mg/Nm³.
● H₂S ≤ 50 mg/Nm³; Total sulfur content ≤ 100 mg/Nm³.
● NH₃ ≤20 mg/Nm³;
● C₆H₆ ≤ 50 mg/Nm³.
● C₁₀H₈ ≤ 50 mg/Nm³.
● Halogen compounds ≤ 50 mg/Nm³.
