process simulation tools

Your process simulation tools do have value, if only that they help you to understand the cement manufacturing process. Many people have developed such tools and they are certainly useful. You will find that companies like FLSmidth and KHD have complex kiln simulation tools which they sell as training tools for use with their control systems and kilns.

Dr Michael Clark

Thanks Michael.

I started writing my own simulation tools when I observed that all my collegues were essentially using simple heat and mass balance calculations combined with additional assumptions.

A typical additional assumption would be: the heat consumption is reduced by so much with an additional preheater stage. Or another: the use of alternative fuels increases the heat consumption in such a way. Or still another: using slag in the raw meal reduces heat consumption. And there are many examples like that regarding heat losses, cooler efficiency, impact of precalcination, ... .

Many of these "known facts", I have been able to discover them "by myself" when I developped my models. I also learned some lessons, like the importance of the exothermic reactions in the burning zone. However, the irony is that once I finished developping the models, I just realized I simply had understood some facts and the long calculations where practically not useful. Why doing long calculations to re-discover simple facts?

But there is more bad news for (my) models! Essentially there are "known facts" that can simply not be simulated or at least would require disproportionate efforts to reproduce them in an ab-initio model. The phase composition - I believe- is one example, although there is a lot of litterature on that. Simply predicting the calcination rate at the rotary kiln input is also beyond the feasability, with all the consequences on the detailled heat and mass balance and temperature profiles. And I even ask myself how realistic the heat exchange calculations could be, considering the complex situation inside the kiln. And what about the heat exchanges during phase transitions, like the liquid formation and the recristalisation in the cooler, and its influence on the heat balance? Do we even know the basic data for such a calculation? And what about burning of tyres?

I think that I might have a new hobby during the coming years. Maybe I will start building a new process tool from scratch. I will focus on heat and mass balancing and not much more.

But the question is still, what would be really useful?

And I have a subsidiary question: what about commercial simulators, why are they not so much used in the cement industry?

Personally I find such process simulation tools usefu, but only as one input to gaining an understanding of the process. We have to bear in mind that they are only a simulation and not the real thing. However, when reality does not correspond with the simulation then that guides us to where the simulation needs to be improved and in that we learn more.

From my perspective there would be 2 principle reasons why commercial simulators find little application in the cement industry:

1. They are expensive.

2. As stated above they are only simulations and do not perfectly correspond with reality, which makes them seem even more expensive and greater luxury.

Dr MIchael Clark