Methods for utilizing the waste heat from high-pressure water in the urea production process
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This post was last edited by 1025199692 on 2015-7-26 08:02. 1. Heating 2. Process heating 3. Power generation through ultra-low temperature waste heat recovery. Taking the high-temperature water in the urea production process as an example, with a temperature of 140°C and a flow rate of 300 t/h, a power generation system based on an organic Rankine cycle for low-temperature waste heat recovery can produce 1,000 kWh of electricity per hour; this saves the enterprise 8 million kWh of electricity per year (assuming 8,000 hours of operation per year), resulting in cost savings of 4.8 million yuan per year (at a electricity price of 0.6 yuan/kWh).
Send a brief introduction to get an understanding of the situation first.
In the stripping process for urea that I am familiar with at present, the preheating of the high-temperature water makes use of distillation towers or a first-stage evaporator, thereby saving steam.
The CO2 stripping units introduced in the early stages used high-temperature water to heat urine in the distillation towers. With the dehydrogenation unit in place, the temperature of the high-pressure scrubber decreases, and accordingly the temperature of the high-temperature water also drops; as a result, the thermal quality is low, so it is more appropriate to generate electricity using a Rankine cycle. How large is the investment? What is the level of maintenance work?
The high-temperature water directly heats the evaporator, while the high-temperature water cooler is almost not used at all; as a result, heat is delivered directly to the urine, resulting in higher efficiency. In fact, this approach saves a significant amount of money on steam costs. When an organic Rankine cycle is used, the various processes involved mean that the efficiency is lower than that of direct heating of the evaporator. If the low-pressure steam generated can be used directly for power generation, the results will be better than those achieved with an ORC cycle. In our case, the low-pressure steam from the low-pressure stage is used to feed the compressor, thereby allowing high-quality high-pressure steam to remain available.
The efficiency of low-pressure steam power generation, air injection into compressors, and Rankine cycle power generation is not high. In the CO2 stripping process, it is best to make direct use of the low-pressure steam supplied from outside, in order to achieve a steam balance across the entire plant. Most factories have excess low-pressure or low-grade thermal energy.
Are there various methods available for making efficient use of low-grade thermal energy surplus?