Gas instrumentation and analysis for the cement industry

Cement production is a complex process, requiring rigor and precision to obtain top-quality products that comply with environmental standards. Controlling the cement plant process, with reliable pressure, flow and temperature measurement instruments, helps to increase efficiency while extending plant life. The analysers gas monitoring system also helps to improve process control while monitoring atmospheric emissions.

Definition of cement and cement manufacturing

Cement is an essential hydraulic binder used in construction, made from ground clinker. Clinker is obtained by firing a mixture of limestone and clay at very high temperatures. The manufacture of cement is a complex process that begins with the grinding of raw materials, followed by their firing in a rotary kiln at temperatures of up to 1,450°C. This chemical process transforms the mixture into clinker, which is then finely ground to produce cement. Used to bind concrete and mortar particles together, cement is indispensable in the construction of buildings, bridges, roads and other infrastructure.

Phase 1: Preparing the raw flour

Raw mill and diaphragm seal

The raw meal mill is used to grind cement raw materials: limestone, clay, silica stone, iron oxide, gypsum and sand. These materials are pre-measured and mixed in the mill. The grinding stage is also an opportunity to add blast-furnace slag from steelworks. Ash from waste incineration plants is also used as an alternative material for cement. The raw materials are then dried with hot gases. Only materials fine enough to pass through diaphragm seal are carried on to the next process. The fine powder obtained is called raw meal.

Electrostatic filter

The electrostatic filter is used to remove harmful particles from the gas. It removes fine particles, such as dust and smoke, from the flowing gas, using the force of an induced electrostatic charge, without preventing the flow of gas through the unit. Because electrostatic filters create little pressure drop and are extensible, they are widely used in large boilers and cement plants. They can handle gases above 350°C and very humid gases. It acts as a final filter, removing particles as small as 0.05 µm.

Phase 2: Burning

Cyclone preheater

The flour must be preheated before being introduced into the rotary kiln. It is introduced into the preheater's vertically aligned heat exchangers. The raw flour swirls down the cyclones in counter-current to the hot gases. As the raw mix descends into the preheater tanks, it is heated to between 800°C and 900°C using the heat extracted from the rotary kiln. In this process, a chemical reaction takes place in the raw flour, enhancing the efficiency of the calcination process. This preheating is necessary to reach the cement's core performance.

Boiler

A boiler is a closed vessel in which water or other fluid is heated or vaporized to supply steam or hot water to other equipment or facilities.
Fire, high temperature gas or electricity are used as a heat source of boilers.
Water-tube boiler : Two drums arranged upper and lower, connected each other by a number of water tubes, through which water is circulated. The tubes are heated by combustion gas to generate steam.

Rotary kiln

The rotary kiln is a tube lined with refractory bricks (3-5 meters wide and 30-60 meters long) that rotates about 3-5 times a minute, and the raw material flows through progressively hotter zones of the kiln towards the flame. The raw flour is heated to 1450°C in rotation. It is then cooled with cold air to form cement clinker. Hot air from the cooler is returned to the preheater to save fuel and energy. Cement or lime depends on the manufacturing process and temperatures involved.

Stage 3: Final grinding

Cement mill

The clinker is then finely ground in a ball mill with other additives (ash from thermal power plants, blast furnace slag or gypsum) to obtain different cement grades. The cement is then stored before delivery.

The importance of gas analysis for air quality

Gas analysis guarantees air quality in cement plants. Thermal power plants and rotary kilns used in cement production emit greenhouse gases, particularly CO2, which contribute to climate change. Gas analysis makes it possible to measure these emissions and implement strategies to reduce them. For example, low-carbon cements are produced using alternative materials and more efficient manufacturing processes, thereby reducing CO2 emissions. This approach is essential for meeting environmental standards and promoting more sustainable cement production.