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Typical control systems that are found in modern power plants must control the many physical aspects of the complex
processes that occur inside the various components of the power plant. As detection and monitoring of pollutants
becomes increasingly important to plant operation, these control systems will become increasingly complex, and will
depend upon accurate monitoring of the concentration levels of the various chemical species that are found in the gas
streams. In many cases this monitoring can be done optically. Optical access can also be used to measure thermal
emissions and the particulate loading levels in the fluid streams. Some typical environments were optical access is
needed are combustion chambers, reactor vessels, the gas and solid flows in fluidized beds, hot gas filters and heat
exchangers. These applications all have harsh environments that are at high temperatures and pressures. They are often
laden with products of combustion and other fine particulate matter which is destructive to any optical window that could
be used to monitor the processes in these environments in order to apply some control scheme over the process. The dust
and char that normally collects on the optical surfaces reduces the optical quality and thus impairs the ability of the
optical surface to transmit data. Once this has occurred, there is generally no way to clean the optical surface during
operation. The probe must be dismounted from the vessel, disassembled and cleaned or replaced, then remounted. This
would require the shutdown of the particular component of the plant where optical monitoring is required. This renders
the probe ineffective to be used as the monitoring part of any control system application.
The components of optical monitoring equipment are usually built in supporting structures that require precise
alignment. This is almost always accomplished using fine scale adjustments to specialized mounting hardware that is
attached to the reactor vessel. When the temperature of these supporting structures increases due to the high temperature
process that is occurring inside the vessel, the optical alignment can often suffer due to the thermal expansion of the
mounting structure. This can render them useless especially for gas velocity measurements or other situations where
precise optical alignment is required.
What is needed is an optical probe that can be inserted into any hazardous environment that will not suffer alignment
problems or other failure modes that are related to high temperature dirty environments, and at the same time maintain a
clean optical surface through the lifetime of the devise so that it may be continually used for optical inspection or for
control system applications. This paper describes details of the construction and the use of a transpiration purged optical
probe which mitigates the problems that are outlined above. The transpiration probe may be used as either an emitter or a
detector. The probe is implemented in the harsh high temperature environment of the NETL pulsed combustion system
where products of combustion and particulate matter have been shown to degrade the performance of a normal optical
window. Assessments of combustion heat release are made by monitoring the ultraviolet signatures that are produced by
the concentration of OH during a pulsed combustion process. It is shown that these measurements are directly correlated
with the pressure within the pulsed combustor. Probe temperature measurements are also presented to show how the
probe and its mounting hardware remain at constant temperatures well below the high temperature environment which
they monitor.
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