PARTICULATE REMOVAL 843
FIGURE 12 Before and after. The photograph on the left shows the typical dense smoke and soot being emitted
from the stack of an industrial oil-fired boiler during the daily tube blowing or cleaning process. The photograph
on the right shows the same stack during tube blowing with an emission control unit in operation.This used with the generalized grade efficiency curve,
Figure 1, and the dust loading correction will give a suit-
able adjustment for changes in operating conditions so that
starting from a guarantee performance at design conditions
corresponding performance for other conditions may be cal-
culated. In essence this establishes a guarantee envelope or
curve to replace guarantee of a single point.
“Outlet stoppers,” that is, low outlet dust loadings to be
accepted as prima facie evidence of satisfactory performance
regardless of actual efficiency, are sometimes included in guar-
antees. The reasons are that isokinetic sampling is laborious
and increasingly imprecise at low dust loadings, and that cer-
tain types of equipment are thought to have inherent limits on
outlet loadings, for example precipitators have rapping losses
which may control overall efficiency in the low loading range.
It is felt, however, that outlet stoppers should be used only
to exclude certain tests of the guarantee and not as evidence
that the guarantee has been met. Cases are known in which
the purchaser desired an outlet loading of approximately .003
grains/ft^3 in order to meet anticipated regulations, but precipi-
tator vendors specified outlet stoppers of .01 grains/ft^3.
Generally speaking, it is desirable to the purchaser to
operate equipment for a number of weeks before making aguarantee acceptance test. Deterioration from factory per-
formance will often occur in such a time span. This time
span should be used only as a shakedown period and not a
life test.
Consideration should be given to the action to be taken
if equipment does not satisfy the guarantee performance,
and a guarantee will usually be the better for spelling out
such remedies. One frequent clause specifies that the vendor
remove below par equipment and refund the purchase price.
This gives considerable incentive to the vendor to meet the
guarantee, but removal of pollution control equipment may
mean complete shutdown or production at a loss of tens of
thousands of dollars per day to the user. Another arrange-
ment is the bonus-penalty clause, under which the vendor
on a sliding scale receives a bonus or pays a penalty if
equipment performs above or below guarantee. At present
the bonus payment aspect is unattractive to the purchaser,
because he receives no benefit from producing less pollution
than the law allows although this would change if a system
of effluent taxation were implemented. Most often the most
satisfactory approach is to require the vendor to upgrade
installed equipment and make additions as needed so that
the guaranteed performance level is reached.C016_002_r03.indd 843C016_002_r03.indd 843 11/18/2005 1:06:47 PM11/18/2005 1:06:47 P