How are the various time periods in the gas production process using the atmospheric pressure fixed-bed batch method allocated?

The gas generation cycle time for the gas stove is set at 150 s, of which 36 s is allocated for blowing air, 0.5 s for cleaning with steam, 35 s for upper blowing, 66 s for lower blowing, 10 s for secondary upper blowing, and 2.5 s for final cleaning

The cycle time is set at 150 s, of which 36 s is for blowing air, 0.5 s for upper steaming, 35 s for upper blowing, 66 s for lower blowing, 10 s for double upper steaming, and 2.5 s for final blowing to clear residue

In this cycle of ours, it takes 135 seconds for blowing, 28 seconds for recovery, 32 seconds for upper blowing, 57 seconds for lower blowing, 8 seconds for secondary upper blowing, and 4 seconds for thorough drying. It’s not absolute; it is adjusted according to methanol production levels.

Method for allocating the cycle time in fixed-bed gasification: The blowing time is determined based on the properties of the feedstock, the requirements of the process, and the size of the associated fans; its purpose is mainly to ensure that sufficient heat is accumulated in the feedstock layer after blowing is completed, so that the gasification layer reaches an appropriate temperature. The time for the secondary top blowing and cleaning phases is generally fixed, as long as it ensures safety and enables the recovery of gas in the furnace. The distribution of time for upper and lower blowing is primarily determined by the position of the vaporization layer; generally, the time for lower blowing is longer than that for upper blowing. If the upper blowing time is too long, it causes the vaporization layer to rise rapidly and get disrupted, resulting in the loss of a large amount of heat, which is not favorable for gas production later on. When the coal quality is good and its particle size is large, the time required for lower blowing to produce gas must be even longer. The specific time for each cycle varies significantly depending on the equipment and manufacturing processes used by different factories; the total time is generally between 120 and 150 seconds.

The process I use here for producing methanol via water-gas synthesis in a fixed-bed system is as follows: First, high-quality raw material coke is conveyed to the respective feed hoppers by coal conveyors, and then fed into the gas generator by an automatic coke feeder where the gasification reaction takes place; the addition of coke is completed during the downward blowing phase. The gasification process consists of six cyclic stages: blowing, steam purging, upper blowing for gas generation, lower blowing for gas generation, secondary upper blowing for gas generation, and air purging. ⑴ Blowing stage: Air at a pressure of 0.128 MPa, supplied by an air blower, is blown in from the bottom of the gas generator. It passes through the carbon layer from bottom to top, where it undergoes a combustion reaction with the carbon layer and releases a large amount of heat. The gas that emerges from the furnace is called blowing gas, with a temperature of around 350°C. The blowing air converges in the main blowing air pipeline before the cyclone dust collector; after being cleaned of dust by this dust collector, it is sent to the waste heat recovery boiler section for heat recovery. ⑵ Steam purging stage: To ensure a low nitrogen content in the water gas, steam is blown in from the bottom of the gas generator for 1–1.5 seconds, thereby displacing the purge air from the pipes. This air then enters the purge air system, converges in the main purge air pipe ahead of the cyclone dust collector, and after being cleaned of dust by the dust collector, it is sent to the waste heat recovery boiler section for heat recovery. ⑶ Upper blowing gas phase: The steam used for upper blowing comes from two sources; one of them is the jacket boiler and heat pipe waste heat boiler in this section. The pressure of this steam is 0.294 MPa, and after superheating, its temperature is around 200°C ； Another portion comes from the steam main, with a pressure of 0.6 MPa and a temperature of 350°C. After depressurization, the two streams of steam are mixed in a steam buffer tank; at a temperature of around 220°C, they are fed in from the bottom of the gas generator and pass upward through the carbon layer inside the furnace, where they react with the hot carbon layer. The temperature of the water gas (upward gas) produced at exit is around 350°C. After dust removal by a cyclone dust collector, the gas passes through a safety tank before entering the water-gas main pipe of the two-hot-tube waste heat boiler; excess heat is recovered in this boiler, reducing the temperature to around 150°C. The gas then enters a gas washing tower, where it is cooled to below 40°C before being sent to the gas holder. ⑷ Downward gas injection stage: After a period of upward gas injection, the hot spots in the carbon layer move upward; to maintain stability in the gasification layer, it is necessary to change the direction of the steam flow, that is, to blow the steam from top to bottom. Low-pressure superheated steam is blown in from the upper part of the gas generator, passing through the carbon layer from top to bottom and reacting with it to produce water gas. The gas coming out from the bottom of the furnace has a temperature of around 250°C; it is fed into the upward gas pipeline and then enters the water-gas main pipe of the two heat-tube waste heat boilers. The waste heat is recovered using these heat-tube waste heat boilers, and after being washed and cooled in the gas washing tower, the gas is sent to the gas holder. ⑸ Secondary top blowing gas injection stage: The process is the same as that of top blowing gas injection. ⑹ Air purging stage: The process is the same as that for the blowing gas. But instead of steam, air is used, with the aim of recovering the water gas in the system. II. Cycle Ratio and Time Allocation: Stage 1 – Blowing with steam for cleaning; Stage 2 – Upper blowing gas and lower blowing gas; Stage 3 – Second upper blowing gas; Stage 4 – Air blowing for cleaning. Remarks: DCS percentage (%): 24, 12, 34, 28, 2. The time allocated to each stage can be adjusted according to operating conditions ； The coal feeding time (8 seconds) is included in the bottom blowing gas. DCS time (seconds) 361.534.563123

• Reference for the source network link: Fixed-bed gasification – process. Using lump coal (10–50 mm) as raw material, advanced fixed-bed gasification processes are represented by the Ruhr process of pressurized moving-bed gasification. Its main advantages include the ability to gasify low-quality coal； High pressurized gasification production capacity ； It has a low oxygen consumption, making it the method with the lowest oxygen demand among the three current gasification methods ； The Ruchi furnace uses reverse gasification; the coal stays in the furnace for up to 1 hour. The operating temperature of the reaction furnace and the temperature of the gas at the furnace outlet are low, resulting in high carbon efficiency and high gasification efficiency. Although the Ruko gasification process has many advantages, fixed-bed gasification can only use lump-free coal as raw material. This not only makes the raw material expensive and results in a low gasification efficiency, but also the counter-current heat exchange between gas and solids leads to a high content of phenols and tar in the crude gas, thereby prolonging the purification process and increasing investment and costs. Fixed-bed gasification – Overview: Atmospheric-pressure fixed-bed coal gasification is a process in which solid fuel is converted into gas using air, steam, or oxygen as gasifying agents. Since the first atmospheric-pressure fixed-bed gas generator was put into operation in Germany in 1882, this technology has continued to be improved. Due to its mature and reliable technology, low investment requirements, and short construction period, it is still widely used both domestically and internationally. It is used to produce gas in industries such as metallurgy, building materials, and machinery. It is used to produce syngas in small and medium-sized ammonia synthesis plants. However, it can be predicted that, as production technologies continue to evolve and corporate production scales expand along with the enlargement of facilities, this gasification technology, due to its strict requirements for raw materials, low production capacity, and high energy consumption, will eventually be phased out over time. The main components of gas produced by atmospheric-pressure fixed-bed gasification are H2, CO, and a small amount of CH4; nitrogen in semi-water gas used in ammonia synthesis is also a component. Gas used as fuel is measured in terms of its calorific value, whereas gas used as syngas is expressed by the volume percentage of CO and H2. Industrial gas is generally divided into air gas, mixed gas (producer gas), water gas, semi-water gas, and medium calorific value gas. Fixed-bed gasification – atmospheric pressure generator gas production process. The atmospheric pressure moving-bed gasification process is a relatively old and widely used gasification method. Its characteristic is that the entire gasification process takes place at atmospheric pressure ； In the gasifier, coal is fed in stages; as the reaction time progresses, the fuel gradually moves downward. It goes through the aforementioned stages of drying, carbonization, reduction, and oxidation, and is eventually discharged in the form of ash and slag, after which new fuel is added ； The operation methods include the intermittent method and the continuous gasification method ； The gasifying agent is usually air or oxygen-enriched air, which is used to react with carbon to generate heat; water vapor then uses this heat to react with carbon, breaking down into gases such as hydrogen, carbon monoxide, carbon dioxide, and methane. (1) Types of producer gas: Producer gas can generally be classified into air gas, mixed gas, water gas, semi-water gas, etc., depending on the gasifying agent used and the calorific value of the gas. (II) Principle of gas production 1. Air gas – Air gas is the simplest production process for producer gas. It uses air as the gasification fuel, and the main chemical reactions are as follows: C + O2 = CO2 – 394.1 kJ/mol; C + CO2 = 2CO + 173.3 kJ/mol. The oxygen in the air supplied from the bottom of the furnace reacts with the hot carbon in the oxidation zone; under ideal conditions, only carbon dioxide is produced, along with a large amount of heat. The hot carbon dioxide gas rises to the reduction layer, where it continues to react with carbon to undergo reduction, producing carbon monoxide and absorbing a certain amount of heat. Carbon monoxide is the main combustible component of air gas. From the perspective of chemical reaction equilibrium, as the temperature rises, it facilitates the progression of endothermic reaction equations, thereby increasing the concentration of carbon monoxide in the generated gases ； An increase in temperature is unfavorable for the exothermic reaction type 2; as a result, the carbon dioxide content in the gas decreases, and when the temperature exceeds 900 °C, the carbon dioxide content in the gas is very low. In terms of the rate of chemical reactions, above 900 ℃, the reaction rate for the combustion of carbon is extremely fast; this process is governed by diffusion, meaning that the diffusion of oxygen to the surface of the solid particles determines the overall rate of combustion. Therefore, increasing the gas flow rate and reducing the particle size of the solid particles helps to increase the combustion rate, with increasing the gas flow rate being the most effective method. For reaction 2 involving carbon and carbon dioxide, its rate is much lower than that of the combustion reaction of carbon. Below 2000 °C, the reaction is controlled by chemical reactions; as the temperature increases, the time required to achieve the same level of carbon monoxide concentration decreases, meaning that the reaction rate increases. By adding the above two reactions, the overall reaction equation for the gasification zone is obtained as follows: C + 0.5 O2 = CO – 110.4 kJ/mol. It can be seen from this overall reaction equation that the main active component of air-coal gas is carbon monoxide. The results of the calculations for air gas in Chapter 2 show that, even under ideal gasification conditions, the gasification efficiency for producing air gas is only 69.3%. The calorific value of this gas is 440 kJ/m³, and carbon monoxide, the useful component in ideal air gas, accounts for only 34.7%; the remaining 65.3% is nitrogen. These analysis results are based on ideal conditions, with pure carbon being used for gasification and the reaction proceeding completely. Even under such ideal conditions, the thermal energy transferred to the gas does not exceed 69.3% of the total thermal energy provided by the carbon. In actual production, due to the loss caused by the entrainment of coal particles, the actual gasification efficiency does not reach the values calculated above; however, it can reflect the difference between the actual gasification process and the ideal process. A large amount of heat is released during the air gasification process, while the reactions that absorb heat are mainly the reduction reactions of carbon dioxide. In addition, there are heat losses due to heat dissipation during the gasification process; this leads to an accumulation of heat inside the furnace, resulting in higher temperatures in the material layer and the gas. This situation makes slag formation more likely, which favors the use of gasifiers that employ liquid slag removal. Other issues include a low calorific value of the gas, high outlet temperatures, and low gasification efficiency – all of which **limit their industrial application**. It is not widely used at present, but it serves as a basis for studying other gasification processes. Fixed-bed gasification – moving-bed gasifier; the moving bed is also called a fixed bed. A moving bed is an older type of gasification device. The fuels mainly include lignite, bituminous coal, anthracite, coke, etc., while the gasification agents include air, air-water vapor, oxygen-water vapor, etc. The fuel is fed in through a coal feeding device at the upper part of the moving bed, and the gasification agent is introduced from the bottom; the fuel and the gasification agent flow in opposite directions, with the ash and slag resulting from the reaction being discharged from the bottom. When the charge is loaded and gasification takes place, using air as the gasifying agent, or using a combination of air (oxygen, oxygen-enriched air) and water vapor as the gasifying agents, the material layer inside the furnace can be divided into six zones, from top to bottom: the air zone, the drying zone, the carbonization zone, the reduction zone, the oxidation zone, and the ash zone. Different gasifying agents result in different chemical reactions. Due to the different gas compositions, temperatures, and the compositions and structures of solid substances in each layer band, the products of the reactions vary to some extent. The main reactions and functions of each layer band in the furnace are different. This post was last edited by Tianya Langji on 2009-2-12 at 11:21 to adjust the font size and remove extra links