Ecology and Economy
Many
process-related operations in the industry produce process gases that in the
past have often been regarded as by-products and have been flared at the
expense of the environment. This practice is changing in light of growing
energy awareness.
Today, even
though they have less energy content than natural gas, process gases produced
in many process-related operations and especially in the steel industry are
being collected in gasometers and used as combustion gas in place of natural
gas in thermal processes. However, the fluctuating composition of the process
gas, especially the CO content and the related fluctuating energy content,
calls for special measures.
The energy
content of the gas composition is stabilized by controlled addition of natural
gas, which is essential for meeting the requirement for a uniform furnace
atmosphere in each thermal process. A high-performance measuring system with
fast response time, consisting of calorimeter and gas analysis, provides the controlled
variable for conditioning of process gases for energy content.
In steel mills
with hot-rolling mills, the process gases produced by the steel mill are to be
utilized as combustion gas in the burners of the downstream hot-rolling mill.
The properties of the combustion gas must meet two very different requirements
for this A defined excess of air must be ensured in the various zones of the
hot-rolling furnace to achieve the desired steel quality. Simultaneously, the
CO concentration in the off-gas from the flue must not exceed a defined limit
since the plant will otherwise be shut down automatically pursuant to the
Emissions Directive. The plant operator must quickly and accurately detect the
changes in process gas composition and, on this basis, add natural gas in a
controlled manner to continuously meet the two requirements. This is only
possible using gas measuring technology with corresponding performance
capability.
Specially
configured analysis system
One measuring
system that is specially configured for this task is the CWD2005 direct
calorimeter from UNION Instruments with additional integrated gas analysis and
measured value processing. The system directly determines the Wobbe index and
gas density values as well as the concentrations of CH4 and C2+. The heating
value and air requirement are also calculated from this. Altogether the
information from the calorimetry and gas analysis is a basis for sufficiently
accurate control of the gas addition. Of particular importance is the higher
air requirement for combustion of alkanes (CH4, C2+, etc.) compared to CO,
which the gas analysis takes into account by determining the concentration of
these two components.
Author / Editor: Torsten Haug* / Wolfgang Ernhofer
http://www.process-worldwide.com/control-and-automation/articles/511448/?cmp=nl-206
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