Low-temperature heat utilization in the distillation section of coking units
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Dear experts, I recently have a tricky task that I really need to carry out. At today’s meeting, my supervisor assigned me the responsibility of designing a system for making use of the low-temperature heat from the distillation section of the coking unit! Good heavens?! I’m just an equipment technician; my knowledge of process-related issues is quite limited. How can I take on such an important task? I’m extremely worried! From what my supervisor said, the idea is to extract the low-temperature heat from the top circulation, middle-stage circulation, and wax oil circulation in the distillation tower through water tanks, and then use it as heat transfer water. This approach can help save both the water used in circulation and the electrical energy consumed by air cooling fans. It can also reduce the amount of steam needed for heating. The supervisor’s idea is good, but as someone who works with equipment, I don’t know where to start. I hope those who have experience with similar modifications can share their insights with me!!!
The low-temperature heat in coking units mainly includes: the waste heat from the oil and gas at the top of the distillation tower, the waste heat from the top circulation, the waste heat from diesel, and the waste heat from wax oil. The temperature of the intermediate cycle oil and the wax oil cycle oil is relatively high, which does not conform to the principle of hierarchical energy utilization; therefore, it is generally not used in low-temperature heat systems. Generally, low-temperature heat utilization is considered from the perspective of the entire plant, rather than just a single device. Low-temperature heat utilization is a highly systematic project that requires detailed process calculations. The existing process flow needs to be modified as necessary, and it cannot be explained simply in a few words if it is to be done properly. You’d better write down the leader’s ideas, think about them on your own, and then assign the task to a qualified design firm.
As mentioned on the 2nd floor, the low-temperature heating requirements for top circulation, diesel, and paraffin oil can be addressed by adding heat exchangers; one can calculate the necessary solutions themselves. The upper part of the tower has low temperatures and high heat, but it is difficult to access; the pressure drop in the pipelines must be taken into consideration, otherwise the benefits will not outweigh the costs, as it will increase the load on the compressor. This requires design by the design department.
I can provide a feasibility study, which might be helpful.
Coking generates a large amount of waste heat, mainly at the top of the distillation tower. The waste heat from the top of the distillation tower, as well as that from diesel, wax oil, compressed dry gas, etc., can be utilized effectively, in addition to the flue gas from the heating furnaces. The waste heat from the vent tower and the waste heat from the cold coke hot water treatment system are difficult to utilize.
The low-temperature heat utilization for various devices is a rather complex and cumbersome process. First, it is necessary to identify the areas where low-temperature heat is required. Since the temperature of the heat transfer water is generally around 95 degrees, it can be used for feeding water into boilers, as a heat source at the bottom of vapor separation towers, and for temperature maintenance via heat tracing. The investment required for second-stage low-temperature heat utilization is generally high; therefore, a proper economic evaluation is necessary, with the internal rate of return needing to be at least 50% or higher ； Thirdly, low-temperature heat utilization is implemented while still ensuring the normal operation of the device without using the heat transfer water system. Let’s stop here for now; if there’s anything unclear, we can discuss it later!
Correction: The internal rate of return in the previous post should be 25%
Has anyone else prepared similar feasibility reports or conducted experiments on their own? I would be very grateful for any advice!!!
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I believe that to develop an effective low-temperature heat system, it is first necessary to optimize the heat exchange network. The heat from higher temperature sources can be utilized within the system or used as a heat source for other devices through heat integration. After that, consideration should be given to gas generation, and only then to low-temperature heat. The boundary of low-temperature heat is not very clear; generally, flow streams are considered to be at low-temperature heat when the temperature is low enough that no heat sink can be found (heat sinks do not include circulating water). For the design of such heat systems, it is advisable to take advantage of pinch point technology, as this ensures that both the flow streams meet the required temperature conditions and are utilized in a hierarchical manner. Water-related factors also need to be taken into account. Additionally, the investment required for heat recovery and the benefits it generates should be considered; generally, an investment payback period of less than three years is considered appropriate. (My personal opinion)
Hey, I also need that information. Could you send a copy to me as well? My email address is *aobai19831005@163.com*. Thank you!