Does it make a difference if the operating pressure and design pressure of the gasifier are different?

Different pressures have an impact on the gasification system. It has a significant impact on gasification equipment, pipelines, and valves. Currently, the main pressures for SHELL applications are also 3.0 MPa and 4.0 MPa. It turns out that the earliest one was the atmospheric pressure K-T furnace. It seems that the two-stage furnaces currently designed also have two pressures: 3.0 MPa and 4.0 MPa. 3.0 MPa is used in the IGCC plant in Tianjin, while 4.0 MPa is used in chemical industry projects.

Using a lower pressure should have an effect on the carbon conversion rate, right?

Designed for high pressure but used at low pressure: first, the coal feeding amount decreases, resulting in a reduced system capacity; it can still be used, but this equates to a lower load, and there are issues with economic viability

Our company recently asked a design firm to prepare a feasibility report, using technology from Tsinghua University – namely a staged gas flow bed. The designed pressure for this system is 4 MPa, while the actual operating pressure is 2.8 MPa; this corresponds to the compressor used later on. We are not sure what the impact of using such parameters will be; please provide clarification. Thank you: handshake

The amount of coal fed in is less, which results in a lower gas production rate; the composition of the gas is also poor, with an increased proportion of CO2. This leads to significantly reduced economic efficiency. Using a pressure level of 2.8 instead of 4.0 poses no safety issues, but it means that the maximum coal feeding capacity can only reach 70% of the designed level, and the quality of the final product will be even lower than that. The economic efficiency is thus very poor

Can lower pressure also result in a reduced coal feeding rate? For a furnace designed with a capacity of 1000 t/year, if the pressure is kept low, then the amount of coal fed will not be sufficient to produce the required amount of gas. However, the designers did not address this issue; they simply opted to reduce the pressure. Additionally, why does the proportion of carbon dioxide increase? Last edited by zhangwei643 on 2007-12-14 17:49]

It is estimated that in order to raise the furnace temperature and reach the same temperature at low load, the proportion of carbon dioxide must be high.

This issue should be analyzed as follows: A low vaporization pressure leads to a decrease in gas density, meaning that the volume of gas per unit mass increases. However, the reaction mixture needs to remain in the vaporization furnace for a sufficient amount of time; therefore, when the pressure is low, in order to maintain the same residence time, it is necessary to reduce the amount of gas produced and thus lower the amount of coal fed in. In this sense, pressure and gas production are essentially proportional. Let’s talk again about the issue of declining gas quality under low load conditions. The gasification system has to dissipate some heat to the outside (through steam generated by the water wall, as well as through the outer walls of the equipment). At low loads, the amount of heat lost through the outer walls remains roughly constant, while the heat lost through the water wall increases due to the thinning of the slag layer. As a result, the proportion of heat loss relative to the total heat generated increases, which in turn leads to a decrease in the efficiency of the cold gas – this is easy to understand.

Personal opinion: 1. The design pressure is balanced and corresponding to the entire system. Under normal circumstances, the design pressure (which is actually the designed operating pressure; the actual design pressure is usually slightly higher than this value to ensure safety) represents the most suitable pressure, and it is not necessary to reduce it. 2. For gasification furnaces, pressure reduction generally leads to the following problems: · A decrease in the furnace’s output ； ·If the operating pressure remains unchanged, reducing the pressure in subsequent stages is a waste of energy ； ·Disrupting the operational balance of the furnace itself can have an impact on its lining ； ·The problems associated with long-term pressure reduction may be even greater; a thorough inspection and testing of the system are necessary when increasing the pressure again ； 3. Based on the above points, we generally do not recommend pressure reduction operations in design and daily production. However, in some cases where partial modifications to an existing system result in a pressure mismatch between different sections and pressure reduction is necessary, efforts should be made to minimize the pressure difference, and certain design measures should be taken to reduce the impact of such pressure reduction operations on the system as much as possible.