Shreekant Hulgi, Vice President at Techport heading Grinding Technology, says that making provisions for inertisation systems is a safe measure, and explains the impor¡tance and various procedures adopted during a process safety audit.
Briefly tell us about process safety audit. How different is it from general safety?
The cement manufacturing process involves an important process phase of coal handling, storage and firing. There exists the danger of fire and explosion in case due protection measures are not in place.
Safety is anything that is protected from danger, risk, threat of harm, loss of personnel/property. Process safety is more concise on origin of risk, threats which come from manufacturing processes involving flammables like solid fuels, combustible materials, etc.
Indicate the process areas or locations that are subjected to process safety audit. In the cement manufacturing process, solid fuel/coal handling, storage, transport, grinding, firing including pyro-processing, hot air generator, etc., are more vulnerable to process risks. Risk of fire explosion is obvious for pressurised systems having fire and carbon monoxide presence. This is normally explained as a ´Fire Triangle´ having three components, i.e., fuel, ignition, and oxygen.
What are the key checkpoints in process safety audit?
Checklists and points are unlimited. However, good, safe measures & practices reduce the risk. Keep safety measures always in mind when you use high volatile solid fuel/ coal. They are risk prone. Process safety checkpoints must start from the raw coal yard, storages to kiln firing. Pyro-processing areas including bag houses must also be checked.
Let us take a case of a coal mill which runs in very hazardous conditions. What are the means to reduce the risk of explosions in the coal mill area?
Coal liberates carbon C during burning which mixes with oxygen O2 to form CO2. This is the burning process in chemical terms. If this combustion is unbalanced or incomplete, then ´CO´ is formed. This is the source of all risk. To prevent and mitigate this risk, we must cut off one of these components - fuel, ignition or oxygen. Spraying of N2 or CO2 gas in this risk prevailing area is called inertisation. N2 and CO2 are good extinguishers of fire. Automatic spraying based on CO temperature measurements protects the whole system.
Tell us something about explosion vents. Where are these located? Explain how these operate to make the process safe through some examples.
When unwanted ignition triggers inside the system, it gradually develops momentum. Because of closed system (adiabatic), this flame becomes high pressure propagation, waiting to burst in open, and comes out as an explosion. Explosion vents are safety equipment installed at key locations which give easy venting to high pressure flame propagation. An explosion vent operates to vent out explosion safely to ambience. This protects the whole system from exploding.
The kiln area generally handles materials at very high temperatures. What are the risks involved and how are these mitigated?
Some of the hot material/handling areas are SLC hot dust, kiln inlet, outlet dust, hot meal sampling, cyclone jam situations, etc. ´Areas access controls´ to prevent unauthorised entrants in and near the kiln/pre-heater area is one of the important measures. Use of high-technology PPEs is a must to prevent any risk. Water and compressed air provisions are a must in every key location. High pressure water pouring on hot material might be dangerous and even cause burning accidents. Good contingency plans must be in place. Operation of air blasters is another area to be careful. Systematic and well approved SOPs (Standard Operating Procedures) must be developed and used compulsorily.