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Industrial fuels oils:—
(B.S.I. Standards)
250 seconds Class E 2.5% to 3.3%
950 " Class F 3.0% to 4.0%
Heavy Class G 3.5% to 4.0%
Bunker Class H 4.0% to 5.0%
15. To use viscosity as a criterion for approval of any fuel oil was considered unwise by Dr.
Forrester, since viscosity is not necessarily a guide to sulphur content, because some 250 seconds
oil from the U.S.A. would contain very little sulphur while some 950 seconds oil from the U.S.A.
might be as good as the average British 250 seconds oil in respect of sulphur content. It will be
noted from the Table set out above that there is an overlap of sulphur content in the various
grades of oil, and on a viscosity standard it could well be that approval would be withheld to a
British oil of 950 seconds with a 3.0% sulphur content, whilst approval would be given to a 250
seconds British oil with a sulphur content of 3.3%. To see the matter in a true prospective it is
necessary to make an accurate assessment of the relative sulphur release of each fuel, since it
may be necessary to burn only half as much of one type of fuel to achieve the same heat release
as another type. For example, the weight of fuel burned to produce a therm of heat is approximately
in solid fuel 8.31 lb., of kerosine 5lb., and residual fuel oil 5lb. Dr. Forrester has explained
this matter in detail, and the following Table sets out his conclusions:—
Sulphur dioxide emitted into air for a therm of heat produced
(Note: All considerations have been taken into account)
Fuel
1 bs.
S.O.2
Kerosine
0.004 to 0.016
Coal (used at gas works)
0.15
Coke (domestic)
0.15
Coke (other uses)
0.15
to 0.3
Coal (domestic)
0.28
Oil fuel (250 seconds)
0.25
to 0.33
Oil fuel (950 seconds)
0.3
to 0.4
Oil fuel (above 950 seconds)
0.35
to 0.4
British oils only are used in the table.
16. In comparing the domestic use of coal and coke with residual fuel oil, it must be remembered
that low chimneys do not facilitate the dispersal of sulphur dioxide, whereas in most industrial
and commercial premises dispersal is facilitated by the taller chimney stacks. The table also
illustrates that fuel oil of 950 seconds might emit less sulphur dioxide per therm of heat produced
than 250 seconds oil, and that a heavy fuel oil could emit less than a 950 seconds oil.
17. If it is conceded that:—
(a) whatever the percentage of sulphur any liquid fuel may contain, it will on combustion
become sulphur dioxide, and be emitted into the air with the products of combustion; and
(b) that sulphur dioxide will ultimately become oxidised to sulphur trioxide and then to
sulphuric acid,and that all three are objectionable as affecting health and materials; and
(c) the removal of all the sulphur from solid fuels remains a problem to be solved because
residual oil fuels are extremely intractable chemically, and no economically feasible
method has so far been found to eliminate or reduce the sulphur content, all of which
would be emitted as sulphur dioxide despite continued research;
the problem outstanding is whether pollution can be reduced by:—
(i) the judicious selection of fuels of the lowest sulphur content for use in selected areas,
e.g., the central areas of large cities with buildings of varying heights, as in the City
of London, or
(ii) by discharging gases through high chimneys to assist their dispersal at high levels with
consequent dilution to comparatively harmless concentrations at ground level?
18. On (ii) above, Mr. Comptroller and City Solicitor is reporting jointly with the Medical Officer
of Health, Mr. Engineer and the Planning Officer to the Improvements and Town Planning Committee
on the powers, if any, possessed by the Corporation to control the height of chimneys of
new buildings, and the prevention or minimising of the nuisance on the products of combustion
emitted from the chimneys of buildings at a lower level to the new and higher buildings.
19. On (i) above, so far as solid fuels are concerned, the question does not arise, since the
sulphur content of such fuels is more or less constant. In the case of industrial fuel oils, apart
from any quality requirements for special industries, the prospective user will wish to use a liquid
fuel which his plant can handle with the greatest economy. This will often be the heaviest, and
therefore cheaper grade, which has the greatest sulphur content. The exceptions to which no
previous reference has been made are the coal tar fuels which consist of distillates from coal
tar, free from admixture of petroleum oils. The sulphur content of such fuels vary from 0.06% to
1.0% which makes them attractive from the low sulphur content, and their use might well be
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