South Africa is in a catch-up phase regarding efficient energy usage and pollution control. Pressure is mounting on industry and local authorities to `clean up their act' by monitoring and controlling harmful emission from combustion processes. Fortunately the necessary instrumentation has become more versatile and compact, making the task easier.
Typical applications for flue gas analysis are boilers, burners, furnaces, power stations, incinerators and heating systems using gas, oil or solid fuels. Gases that require monitoring during combustion are:
Carbon dioxide (CO2)
Carbon dioxide is the result of complete combustion. The maximum achievable concentration (CO2 max) depends on the fuel being used. CO2 monitoring provides a measure of combustion efficiency.
Carbon monoxide (CO)
Carbon monoxide is a result of incomplete combustion. The gas is colourless and odourless, and is extremely dangerous for human beings - a concentration of 12 500 ppm (1,25%) leads to death within a few minutes. Reasons for CO emission - insufficient air, excessive airflow - or cooling of the flame before complete combustion has taken place.
Carbon (C)
Carbon-C results from incomplete combustion and soots-up the chimney.
Unburned hydrocarbons (CxHy)
Unburned hydrocarbons are formed during incomplete combustion and contribute to the greenhouse effect.
Oxygen (O2)
Oxygen is consumed during combustion. The remaining oxygen is a measure of combustion efficiency.
Nitrogen oxide (NO)
In case of high temperatures, nitrogen combines with oxygen, forming nitrogen oxide. This is a respiratory poison that damages lungs.
Sulphur dioxide (SO2)
Sulphur dioxide is formed during combustion of coal and oil. If the flue gas temperature drops below the dew point, Sulphuric acid is formed which soots-up the chimney and pollutes wastewater.
Some parameters related to flue gas analysis are calculated from the above measurement results. These include:
QA:
* Flue gas heat loss.
* The ratio of excess oxygen to the theoretical air requirements.
effn and effg:
* Net efficiency and gross efficiency relate to the calorific value of the fuel and the latent heat of water vapour contained in the flue gas.
In the past the inhibiting factor for flue gas analysis has been the capital outlay for equipment. Recently developed instruments use location-independent condensation traps and filters to protect the cell. New electrochemical gas sensors offer rapid availability of the measured values, small space requirements, maintenance by the user and low manufacturing costs. However, a great deal of development work is necessary to create suitable measuring cells. Allowance has to be made for cross-sensitivity. The layout of the gas path is a major consideration when designing portable flue gas analysers. Another practical aspect is the ease of replacement of cells.
A leading manufacturer in this field is Testo (Lenzkirch, Germany). Testo specialises in portable instruments. The range includes entry-level units for single gasses to highly complex systems for longer term monitoring of power stations above 500 kW.
The recently developed Testo 350 measuring system offers simultaneous flue gas analysis at different measurement points. Data can be logged and downloaded via a databus for analysis on a PC or the control instrument. The system overcomes the difficulty of accessing measuring points, which are cumbersome to reach due to hot and awkward locations. (The control display is detachable and can be installed at the burner control panel.)
Parameters that this instrument is able to monitor include differential pressure, velocity measurement, temperature, humidity, volume flow, indoor air quality, pressure, rpm, current and voltage. The Comsoft software permits automated or manual measurements to be taken at specified times, or when triggered by a signal. It also allows online measurement with curves, tables, histogram and the option of showing the readings from the different analysis boxes in system graphics. Testo's 350 is also portable.
Testo offers a two-year warranty on its flue gas analysers. To the customer this represents a significant saving in maintenance costs. Testo will also provide a service for measuring instruments up to 15 years old. South African companies that have benefited from Testo flue gas analysers include Iscor, Polifin, Steinmüller, various Technikons, Daimler-Benz and Volkswagen. Testo is represented in South Africa by UniTemp.
For more information contact Heidi Herwig, UniTemp, 011 392 5989, www.unitemp.com
© Technews Publishing (Pty) Ltd | All Rights Reserved
printer friendly version