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Re: Municipal solid waste incinerator
I wrote an individual note to Lynda on this, but I thought a general
letter to the group would be appropriate.
Lynda described a municipal solid waste incinerator (MSWI) that was
going to increase operations to seven days a week from the current five
days per week. The operating authority said that the startup and
shutdown phases had upset conditions that produced more pollution such
as dioxins, and that operating all week would reduce the emissions from
these two conditions (except under the obvious cases of maintenance
when the plant is shut down, then restarted). She said the control
technology was a baghouse.
The MSWI generally has more emissions during startup and shutdown, that
is correct. The upset conditions are more likely to occur at startup
and will last from ten to twenty minutes depending on operator
training, the type of incinerator, and how easy the process is to
control (in some cases over-automation actually makes controlling this
much harder from an operator standpoint). In addition to saving some
emission problems, the facility is eliminating stress brought about by
the condition changes to the system. E.g. it is eliminating a number
of times the facility is brought up to operating temperature, then
cooled down to ambient temperatures.
However, the facility's reasoning probably has more to do with burning
more trash, in this case a 20+% increase in overall throughput to the
system. Normally, this is not a big deal for many types of facilities.
Except here, the MSWI may have only one form of control technology - a
baghouse. I don't know how accurate the description is, but if true,
then a lot of pollution will just increase 20%, which would more than
offset any savings made by eliminating those startups and shutdowns.
The baghouse does not control oxides of nitrogen (NOx), volatile
organic compounds (VOCs), and carbon monoxide (CO). Many products of
incomplete combustion (PICs) are also VOCs and would not be collected.
Many semi-volatile organic compounds will pass through, how much
depends on the temperature in the baghouse - which includes dioxins and
furans. And the source may not be collecting acid gases or sulfur
dioxide (SO2) (depends on if lime injection is used or not). Its
collection of mercury emissions is usually very poor, and depending on
the temperature of the baghouse, may not collect cadmium, lead, and
hexavalent chromium too well either.
To be fair to baghouses, they do collect 99+% of the particulate
pollution sent through it if it is correctly sized and properly
If this is the only control technology on the facility, then the
operating agency is just waving mirrors in an attempt to increase
throughput to the system. On the plus side, if an operating increase
such as this is requested, it may provide the means of legally forcing
the company to install more control technology that would more than
offset any increase in operations, such as a venturi scrubber followed
by a packed-column scrubber. This type of scrubber installation would
reduce much of the above by 99% or better, but still have a problem
with NOx, CO and some VOCs. VOCs and CO are best controlled by good
operating practices; NOx requires a revised combustion chamber (not
likely) or a selective catalytic reactor (SCR) (expensive).