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39
assessed as against that of industrial processes, which generally continue to be of
the same order of intensity throughout the year. Nevertheless, the inefficiently
operated industrial plant can be a great nuisance from the smoke emission aspect.
As to the possible future diminution of this, on the domestic heating side, apart
from the replacement of old grates by properly designed appliances, the main hope
is in the increased use of gas or electricity or smokeless fuel. On the industrial side
it must be by the proper control of firing and draught conditions and by the provision
of special attachments where necessary for giving a more flexible adjustment
of draught when firing is being done. As also applies still more to the next section
on ash or grit, the provision of a suitable type of fuel for the particular furnace and
an increase in the provision of washed coal would be advantageous.
(b) Ash and Grit. The proportion of this from domestic fires is only small, it
being mainly industrial in origin. The prevention of it (by e.g. electrostatic precipitation
and grit arresters) is reasonably easy and should be increasingly adopted.
(c) Sulphur gases.— The reduction of these is the most difficult problem. Something
can be accomplished by an increasing use of coal washing before delivery to
the consumer since this removes some of the extraneous sulphur-containing compounds.
Otherwise the normal burning of coal will inevitably emit the oxidised
sulphur into the atmosphere : no removal process from flue gases on a small scale
is feasible. For large consumers such as electricity generating stations gas washing
processes have been devised which have attained an efficiency of removal of 90-95
per cent. In fact two large power stations (Battersea and Fulham) were operating
on two rather different processes before the last war, having been statutorily required
to do so as the result of public enquiries. The washing lapsed during the war and
no part of it has yet been resumed at Fulham: at Battersea 30 per cent, was in operation
up to June, 1949, and 70 per cent, at the end of the year. Unfortunately the
average efficiency of removal has recently been relatively poor in this case and, in
view of the cooling effect of the process on the effluent gases, and consequently more
rapid diffusion downwards, it is essential that a high percentage of removed shall be
maintained if the procedure is to be of benefit to the surrounding areas as far as
sulphur gas reduction is concerned. This question of the formation of relatively high
local concentration of sulphur gases in the neighbourhood of large coal consumers
is of importance even when taking into account the increased diffusion effected by
the use of tall chimneys. The increase in such concentrations of use is of interest as
evidenced by the fact that, for the whole country, in 1938 only 8 per cent, of the
total coal consumed was used at electricity generating stations, whereas in 1949 the
figure was 15 per cent. The contrast is even more striking in the case of London
where calculation from the Ministry of Fuel and Power's Statistical Digest shows
that 27.7 per cent, of the sulphur pollution in the London region originated from coal
burnt at electricity generating stations: this estimate takes into account the fact
that the coal supplied for these stations is, at least in some cases, of special quality
with a low sulphur content. The actual proportion of coal burnt is somewhat higher.
It must, of course, be emphasised that the power produced by the use of this coal
at the stations will be employed elsewhere in lieu of burning coal and producing
sulphur gases in the process ; but the local concentrations caused in the areas around
the stations need careful consideration especially bearing in mind the continuing
programme of extensions and new construction of stations. It must also be borne
in mind that the old processes of gas washing are very expensive and the results of
the investigations now being conducted by a working group (of which the Chemistin-Chief
is a member) under the auspices of the Department of Scientific and Industrial
Research on the possible development of a new method for the removal of
sulphur compounds from industrial gases are awaited with much interest.