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Correcting the poor manufacturing practices of excessive primary air supply and overly high temperature of steam entering the furnace. Author/Source: Zhengda Thermal Energy. Date: 3-19-2008. File location: file:///E:/DOCUME~1/zzjjaa/LOCALS~1/Temp/ksohtml/wps_clip_image1.wmf. The appropriate amount of primary air is 19×103~26×103 Nm3/h for Φ3.0 furnaces, and 22×103~29×103 Nm3/h for Φ3.2 furnaces; this is because the wind speed in the gas generation furnace should be between 0.7~1 m/s. However, in reality, the actual value at our site is 27.6~40.5×103 Nm3/h, which is clearly excessive； The appropriate steam parameters for entering the furnace are 0.1±0.02 Mpa at dry saturation, as this ensures that when the steam enters the upper and lower chambers of the furnace at pressures of around 20 KPa and temperatures above 200°C, it will not condense (the dry saturation temperature of this steam is 120°C). However, in our actual operation, the parameters are 0.1±0.02 Mpa and temperatures of 140–240°C, which is clearly too high. Excessive air blowing and excessive steam fed into the furnace lead to overheating, resulting in low production capacity and high energy consumption in the gas generator. The gas generator is a reaction heat exchanger, where chemical reactions and heat exchange take place simultaneously within the same furnace. During the blowing phase, the oxidation of carbon occurs in the combustion zone, while the reduction of CO2 takes place in the transition zone ； The heat exchange effects between carbon and flue gas, as well as between ash and air, occur in the transition layer, the red carbon layer, and the ash layer, respectively. During the gas production stage, the decomposition reaction of steam by high-temperature carbon takes place in the gasification zone; this gasification zone is equivalent to the combustion zone and the transition zone in the blowing stage. The heat exchange between the superheated wet gas and the unreacted steam with the carbon and ash occurs throughout the entire ash layer and carbon layer. 1. The combustion reaction occurs at an extremely fast rate, with a large amount of heat being released. During the blowing process, the reaction O2 + C = CO2 + Q takes place in the combustion zone. The reaction is characterized by: (1) an extremely fast rate, resulting in a very thin combustion layer of only about 100 millimeters thick. (2) The reaction is very complete, so all of the O2 is converted into CO2. (3) The temperature is extremely high, so the temperatures of the solid carbon and ash rise to their melting points, beyond which they can no longer increase, namely around 1300℃ ； The temperature of the gas phase (CO2+N2) can be raised to ~1800°C, thereby increasing the temperature of the carbon in the transition layer closest to the combustion zone, as well as the temperature of the ash and grates located below it, which are also closest to the combustion zone. The reduction reaction CO2 + C = 2CO – Q occurs in the transition layer while blowing air. The reaction characteristics are as follows: (1) It is highly dependent on temperature, showing almost no reaction below 900°C. (2) It depends highly on the activity of the carbon, so the reaction takes time to proceed. (3) This reaction requires heat from carbon. The thermal benefit during blowing occurs in the combustion zone; the heat of reaction goes to the reaction products, that is, CO2 and ash possess all the heat of reaction. However, heat is transferred rapidly, and at the same time, the unburned carbon as well as the N2 in the air receive the corresponding amount of heat. The heat is retained by the carbon and ash, while CO2 and N2 are carried upward in the flue gas along with the heat. The carbon and ash remaining after heat storage emit heat in all directions due to the high temperature, raising the temperature of the ash at the bottom as well as the carbon in the filter layer above. The flue gas moving upward, being at a higher temperature, also emits heat in all directions; as it moves upward, it transfers heat to the carbon in the transition layer first, further increasing the temperature of that carbon. A carbon layer whose temperature is raised above 900°C is generally referred to as a transition layer. Therefore, the transition layer is also thin, with a thickness that is only 1.5 to 2 times that of the combustion layer. 2. The gasification reaction requires extremely high temperatures as well as a long contact time between the reactants. During gas production, there are two main reactions: H2O + C = CO + H2 (1) and 2H2O + C = 2H2 + CO2 (2); these reactions take place in the vaporization layer at the highest temperatures. About 75% of them involve reaction (1), and higher temperatures are more favorable for reaction (1) ； ~25% of the cases involve reaction (2); the greater the excess of steam, the more favorable reaction (2) is. The reaction is characterized by: (1) it consumes a large amount of heat and is highly dependent on temperature, with virtually no reaction occurring below 900°C. (2) It is highly dependent on the activity of the carbon, so more contact time is required for the reaction to proceed. Precisely because the reaction requires high temperatures and heat absorption, as well as a prolonged period of contact, under reaction conditions such as those in a fixed-bed furnace, the decomposition rate of the steam fed into the furnace usually only reaches around 50%. The heat effect during gas production occurs in the vaporization layer, where the reaction is endothermic. The wet gas, composed of the gas produced by the reaction and the unreacted steam, receives heat in the gasification zone through radiant heat transfer from the carbon as well as convective heat transfer between the gas flow itself and the carbon, thereby becoming superheated before leaving the gasification zone. When superheated wet gas passes through layers of red carbon or ash that are at a lower temperature than itself, it transfers some of its heat to them.