Why Sulphur Plants Plug
Plugging of piping and vessels within modified-Claus sulphur recovery units is extremely common, and the causes are often poorly understood and the proper solutions often improperly implemented. In some cases, the plugging causes additional pressure drop through the sulphur plant, resulting in reduced sulphur plant capacity and possibly limiting the gas plant or refinery throughput as well. In other cases, it results in complete blockage of parts of the sulphur plant, often meaning an unplanned shutdown, high SO2 emissions, expensive turnaround costs, and lost gas plant or refinery production. The first step in dealing with sulphur plant plugging is to have the proper monitoring methods to detect plugging, the right tools to locate where the plugging has occurred, and the right methods to analyze the plugging material in order to determine the root cause(s) of the plugging. The most common root causes of plugging include: soot formation from poor stoichiometry during fuel gas startups and shutdowns; ammonia salt formation from poor reaction furnace destruction and / or over oxidizing process environments; alumina dust from refractory or catalyst pieces and fines; iron based corrosion products from a variety of corrosion mechanisms; and frozen or high viscosity sulphur from incorrect process temperatures or incorrect vessel insulation / heating. The key to avoiding plugging is to understand and avoid these plugging mechanisms in the first place, and processing, design, and procedure options for each of these areas are discussed in this paper. In addition, some of these plugging mechanisms can be reversed on line, and recommended reversal procedures are also covered in the paper. The paper will include actual case studies from a wide variety of gas plant and refinery sulphur plants from around the world.