Page 46 - Materials Chemistry, Second Edition

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Cleaner Production
liquid oil produces high temperature gases causing the formation of NO x ,
which is hazardous to the environment. In addition heavy oil has low combus-
tion efficiency producing a high percentage of hydrocarbon with the exhaust.
However, natural gas does not contain (or contains a very low percentage of)
sulphur, heavy metals and impurities and emits lower levels of NO x and
CO x . Using natural gas instead of heavy oil or other fuels will lessen the pol-
lution because natural gas is more environmentally friendly. Moreover it
will increase the efficiency of the combustion process. In order to achieve
this switch from heavy oil or other types of liquid/solid fuel to natural gas,
a change in combustion equipment is a must.
Another example for this technique is Wiggins Ltd, a company that
operate a paper mill with a large output of waste water with consequent high
charges for its disposal in the public sewage network. As a result a cleaner
production industrial audit decided to replace the water lines, recycle cooling
water, and install backwater tanks. This was a partial change in the process,
its control and operation. It resulted in a 77% reduction in water consumption
with overall reduction in cost (Williams, 1998).
In yet another example dealing with the food sector where very high
water consumption was observed and measured during the washing process,
it is always recommended to install high-pressure and low-volume spray
nozzles to guarantee a good cleaning process with less water consumption.
In the textile sector, with high energy and water consumption during wet
processes, it is always recommended to use countercurrent flow rather than
co-current flow to save water and energy as will be explained later in the
case studies.

Technology change: Technology change is oriented towards processes modi-
fications to reduce raw materials, water, energy as well as wastes and emis-
sions, and ranges from minor changes that can take place in a process at low
cost to the change of the whole production process that requires large capi-
tal investment. In other words, technology change involves replacing one
process with another that could be less energy consuming or more efficient.
For example, cement is produced by mixing limestone and clay together with
some other additives in a dry or wet process, so using the dry process tech-
nology would consume less energy. Either production techniques can be used.
To get the final product, the wet process requires evaporating water after
mixing – this evaporation process consumes a large amount of energy – while
the dry process requires less energy producing fewer air pollution emissions.
Technology change using cleaner production techniques is always recom-
mended as a last option.

Input material change: Input material change involves substituting one mate-
rial for another which is less harmful to the environment, more feasible to use
and has the same or better technical requirements. In the textile industry,
for example, sulphur black dyeing, as will be explained later in detail, is