FROM RAW MEAL TO CLINKER
Our visit to Hope Cement Works wasn’t only to the control room, we were very excited to see the entire plant. During our tour, we were taken up to the top of the preheater tower where raw meal from the quarry is fed at the top of the preheater tower once it has been homogenised in a silo. From there the raw meal will start going down the cyclones, heating up as it goes down with the gases from the kiln and the bottom cyclone burners. Hope uses four cyclones for each of their kilns. These are huge and imposing metal funnels that transmit tens of tons of material every hour. Unlike many of the cement plants our team works with, Hope doesn’t have a precalciner. This is because the precalciner is a fairly new addition to cement plants, and older plants tend not to have one. Precalciners make the process more efficient but retrofitting them is extremely challenging as it requires moving or changing most of the other components of the plant.
As the raw meal heats up into “hot meal” the calcination reaction starts. At 800ºC+, the meal is calcined and goes to the kiln after spending less than a minute in the cyclones. The unique raw meal used by Hope reaches temperatures of 1550ºC in the kiln – higher than a standard ~1450ºC a cement plant would heat its hot meal to.
Walking between the two kilns, we could feel the heat build as we approached the burning zone, the hottest part of the kiln and of the whole plant. It cooled very quickly as we marched towards the outlet of the kiln.
The red hot clinker falls out of the kiln into the cooler causing the clinkerization reactions to stop. The heat from the clinker can then be recycled as the process repeats. The moving clinker bed bubbles away as fans push air from beneath to get the most heat out of the clinker.
From there the clinker is then cooled naturally in a silo where it can then be homogenised.
Finally, the clinker is poured inside the grinder. This is the last step before it is packed and shipped off directly by train (Hope has the advantage of having a railway on site) to be used by builders and property developers all over the UK.