Gas Measurement in Cement Plants

Cement production generates more carbon emissions than any other industrial process, accounting for approximately 5% of global emissions that include carbon dioxide (CO2), nitrous oxides (NOx), and sulfur dioxide (SOx). Luckily, there are strong monetary and environmental incentives for conserving energy and reducing NOx, SOx, and CO2 emissions from the cement manufacturing process.

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Cement Plant Gas Metering Applications

Stack Gas
Gas entering the stack must be measured for remaining oxygen, unburned fuel, pollutants and particulates.

Gas Characteristics:
Hot, moisture, high rate, particles and grit
Cogeneration
Heat energy, fuel or steam must be measured as it drives the cogeneration turbines to ensure a balanced boiler or combustion chamber.

Gas Characteristics:
Heat, moisture, high pressure, high rate
Fuel Air
Air used to transport coal dust must flow at certain rates. Mass flow must be measured precisely to allow the proper air/fuel blending in the combustion chamber.

Gas Characteristics:
Particles, heat, erosive, combustible
Sorting and Conveying
Air is used to convey cement particles and separate them into different sizes. Precise air pressure control is required to ensure proper transport and classification.

Gas Characteristics:
Pressurized, particles
Clinker Cooler
Ambient air is forced up through the clinker cooler grates, transporting the heat away as rapidly as possible. The heated air is piped to the preheater tower to heat the incoming cement meal.

Gas Characteristics:
High rate, high pressure
Kiln Air
A powerful jet of air is pumped into the kiln to be mixed with fuel for combustion. The rate of flow determines size and shape of the flame as well as the amount of hot gas being sent to the preheater tower.

Gas Characteristics:
High rate, high pressure
Kiln Fuel
A large volume of fuel is piped into the kiln to be mixed with air for combustion. The size and position of the fireball and kiln temperature are controlled by the fuel stream.

Gas Characteristics:
High rate, high pressure, particulates, dust
Cooler Exhaust
Excess hot gas from the clinker cooler is piped to the preheater tower. Monitoring the gas flow is necessary to monitor heat transference, to control the heat in the preheater cyclones and to measure overall plant efficiency

Gas Characteristics:
Extreme high heat, particulates, dust
Precalciner Fuel
Fuel is piped into the base of the Precalciner to be mixed with air for combustion. Control of temperature is important for sintering the raw meal so careful measurement of fuel is required.

Gas Characteristics:
High rate, high pressure, particulates, dust
Precalciner Primary Air
Air is blown into the base of the precalciner combustion chamber to be mixed with fuel and burned. Careful control of the flow rate creates a fireball of the right size and temperature. Too hot and the furnace can be damaged, too cool and the fuel and oxygen are not burned completely.

Gas Characteristics:
High rate, high pressure
Precalciner Overfire Air (Secondary & Tertiary)
Air is piped into the Precalciner above the main combustion zone to extend the fireball higher in the chamber, spreading the heat farther and more completely burning the fuel.

Gas Characteristics:
High rate, high pressure
Combustion Gas
All heated gas used in the cooling tower comes from the kiln, clinker cooler and pre-calciner. After it’s travelled up through the tower and heated the incoming cement meal it’s exhausted from the top of the tower. Monitoring this flow tells you the efficiency of combustion, effectiveness of filters, leakage, and pollutant levels.

Gas Characteristics:
Superheated, high pressure, high flow rate, moisture, particulates, erosive, corrosive.
Stack Emissions
Many cement mills run continuously, 24 hours per day. Stack emissions may change day by day due to changes in raw materials and fuels. Constant Emissions Monitoring is required on the exhaust stack. Dust, oxides, organic compounds, acid gases and trace metals must be monitored and quantities reported regularly.

Gas Characteristics:
Heat, particulates, moisture, erosive, corrosive, high volume, high duct size
Stack Emissions
Many cement mills run continuously, 24 hours per day. Stack emissions may change day by day due to changes in raw materials and fuels. Constant Emissions Monitoring is required on the exhaust stack. Dust, oxides, organic compounds, acid gases and trace metals must be monitored and quantities reported regularly.

Gas Characteristics:
Heat, particulates, moisture, erosive, corrosive, high volume, high duct size

Coal Plant Gas Metering Instruments

Primary Air

In cement plants primary air is used to drive combustion in the kiln, precalciner and possibly a cogeneration boiler. Primary air is pumped into the base of the precalciner and mixed with fuel for initial combustion. It is jetted into the rotary kiln with a powerful stream of fuel to create a fireball over the clinker and heat the kiln up to 14800 °C. Primary air may also be sent to the powerhouse where it is used in combustion for power generation.

Combustion Gas

Superheated gases from the kiln and the grate cooler are circulated to the raw mill for de-dusting, the preheater towers to heat the incoming raw materials, to the decalciner, to dryers to dry coal fuel, to cogeneration stations to be used in generating power and finally sent to the exhaust stack. For maximum efficiency and leak detection the hot and particle laden gas may be measured as it exits the combustion chamber and cooler, the preheater outlet, baghouse and as it enters the stack.

Stack Gas

Traditionally a dirty industrial process, cement manufacturing produces high volumes of greenhouse gases and particle laden air. All cement plants are required to monitor and report emissions under a certain threshold. To meet this requirement numerous recirculating and re-burning procedures are in place, as well as filtering and scrubbing. Unfortunately the scrubbing process used to remove Nitrogen Oxide and Carbon Dioxide from exhausted cement gas introduces a lot of moisture. This hot and moisture laden gas may still contain unburned fuel and cement particles. Stack gases from cement plants are hot, large volume, condensing, with particles and moisture droplets coalescing in the stack and falling down as rain.