The issue of steam production in the Ruchi synthesis tower
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We use a process for producing methanol from coke oven gas, and the operation has not yet begun. The steam generated in the synthesis tower’s drum enters directly into the medium-pressure steam network. This network is designed for a pressure of 2.5 MPa; according to the relationship between steam pressure and temperature, the temperature of steam at 2.5 MPa should be 226 degrees Celsius. Therefore, the water temperature inside the shell of the synthesis tower must be higher than 226 degrees Celsius, due to heat losses. The syngas temperature in the tube side will definitely be higher than the temperature of the shell side water. (Otherwise, there would be no heat transfer.) We know that at the beginning of catalyst use, the outlet temperature of the synthesis tower is roughly 220 degrees Celsius, and the steam pressure generated is less than 2.3 MPa; as a result, it’s possible that the generated steam cannot be sent to the steam distribution network. Dear sea friends, can steam be generated properly? Which of your companies’ synthetic steam drums supplies steam to the medium-pressure steam network, and what is the pressure in that network? Does it fit this correspondence?
Saturation steam pipelines are generally used solely to supply saturated steam to turbines for power generation; they are not intended as other sources of power. Therefore, the pressure requirements for such pipelines are not very strict. Additionally, factories install these pipelines mainly in order to make use of the waste heat steam generated by the synthesis reactors, so the operating pressure of these pipelines should be adjusted to match the pressure of the steam drums in the synthesis towers. So when the initial temperature of the catalyst is low, it’s sufficient to keep the pipeline network pressure lower!
Our medium-pressure steam network supplies steam for conversion processes, and it is essential to maintain the proper pressure.
If there is a pressure limit on the steam pipeline network, the exit temperature of the synthesis tower will naturally increase, reaching approximately 245°C. Otherwise, the only option is to reduce the pressure in the steam drum in order to control the outlet temperature at 220°C.
It is best to configure it as a dual-control system; at the initial stage of catalyst use, steam should be supplied from a 0.8 MPa steam network (which can supply the methanol distillation unit)； In the later stages of operation, once the drum pressure exceeds 2.3 MPa, it is connected to the medium-pressure steam network.
The temperature control in your reactor is a bit too low. We also use Luchi catalysts, and the outlet temperature is kept at 230 plus or minus 1 degree. You might want to consult the catalyst manufacturers; among those domestic catalyst suppliers, there are a few that keep the temperature at the lower limit required for catalyst activation, but this approach is unstable – the temperature needs to be increased after just a few days. Moreover, there is a considerable amount of wax in the product. We have also tried using 220, but it’s not easy to operate, and sometimes the amount of synthesis by-product is quite large. Hydrogen recovery is not feasible; it can only be vented.
We use the coke oven gas to produce methanol, with C307 as the material; it has taken almost two years for the outlet temperature to reach 228 degrees Celsius. I asked some people, and there were various opinions on this issue. Generally, as the water in the shell circuit circulates, the temperature of the drum decreases by 3-5 degrees Celsius due to heat loss; the pressure acting on the water in the shell circuit is 0.5 kilograms higher than that on the water in the drum, which results in a higher temperature for the water in the shell circuit. I’m quite worried that steam won’t be able to be delivered from the synthesis drum, given the need to maintain an outlet temperature of 220 degrees Celsius in the synthesis tower. Please give me some advice.
Replying to the person above: Our medium-pressure steam network is used to supply steam for conversion processes, and it is essential to maintain the proper pressure. May I ask, Yangzijiang, what is the pressure of your conversion system? What is the minimum allowable pressure for steam? If the steam pressure required for your conversion process is around the level of the steam generated in the synthesis tower’s drum, it will be difficult to meet your steam requirements, which could affect the operation of methanol synthesis!
The pressure in the converter is generally around 1.9 MPa.
It’s normal if it can’t be sent out; in that case, the outlet temperature of the synthesis tower needs to be increased, but the circulation rate must also be maintained. C307 is still okay; you can talk to the manager at the same factory – there should be no problem.
Using domestic catalysts, it is definitely not possible to produce 2.5 MPa medium-pressure steam as a by-product in the early stages of catalyst use. It is best, as suggested on the 5th floor, to equip it with pressure pipelines of two levels to facilitate switching between different periods. Some plants are equipped with a steam network at 1.3 MPa, to which the medium-pressure steam generated by the synthesis tower is sent.
The outlet temperature of the synthesis tower isn’t increased arbitrarily; it can’t even be raised by 1 degree in a month. Otherwise, the catalyst will age faster.
We use catalysts from abroad; the steam generated as a by-product of synthesis is not fed into the medium-pressure pipeline system but rather into the low-pressure pipeline system. We have not yet reached full production capacity, and the steam pressure in the drum is still below 2 Mpa. The outlet control valve is of foreign origin and has pressure reduction capabilities.
The problem is that, according to the process design, if the by-product steam from the synthesis tower cannot be fed into the medium-pressure steam network used for conversion, there will not be enough conversion steam at full load.
Can the converted steam drum not provide some medium-pressure steam? The steam used for synthesis and restart in our plant comes from the low-pressure pipeline network
Are you involved in natural gas steam reforming? If so, a steam pressure of 2.2 MPA is sufficient for the conversion.
Whether the steam generated by the drum can be fed into the pipeline network depends on the operating pressure of the medium-pressure pipeline network. If the conversion pressure for coke oven gas is 2.0 MP, then the medium-pressure pipeline network can be maintained between 2.15 and 2.25 MP; if the pressure in the steam drum is lower than that of the medium-pressure pipeline network, it is depressurized to the low-pressure pipeline network.