Problem No 14: High synthesis operating pressure

Operating at the wrong synthesis operating pressure is always a tricky situation for any urea plant operator, knowing that operating at too high a pressure will lead to the pressure safety valves blowing off. Such an incident would not only cause a significant environmental impact but also a forced shut down of the plant as typically the pressure safety valves no longer close properly after blowing. Servicing these valves becomes necessary and plant down time can be a costly incident. On the other hand, operating at too low a synthesis pressure will lead to lower conversion figures, higher carbamate recycle streams and higher energy costs.

The key is to measure the synthesis pressure in a reliable way. In an ideal situation, the synthesis pressure would be measured as close as possible to the pressure safety valves, e.g. in a high pressure carbamate gas line. Until recently this was not possible because of the risks of crystallization and corrosion so the synthesis pressure has mostly been measured at locations where these risks are absent or less likely.