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The big challenge in the cement industry - Digital gas flow measurement

Published by , Digital Administrator
World Cement,

Modern Cement Plants have many locations where an accurate measurement of gas flow is essential for the optimised control of the process. Whether it be the correct operation of the draught fan downstream of a downcomer in order to run the kiln air flows correctly or the tertiary air flow into the calciner process, the correct gas flow is often the key to an optimised setting of essential process parameters.

In the cement industry, pressures as well as temperatures have often been used to calculate the process gas flows, however this method leaves large uncertainties about the real flows of gas as well as enthalpy in the process.

Today the following processes in the cement industry are of special interest when it comes to process gas flow measurement:

  1. Downcomer on kiln preheater: Here the better control of the ID fan downstream is of interest, especially in getting better control over the O2 content of the kiln off gas.
  2. Raw mill gas flow: here the interest is the milling process but also the prevention of over or underdrafting the mill. In several applications the overall power consumption of the mill fans could drastically be reduced.
  3. Tertiary Air Duct: here the interest is the correct operation of the calciner as well as the right amount of bypass air around the kiln in order to reduce NOx whilst keeping the rotary kiln at the right stoichiometry.
  4. Bypass: in order to measure the bypass amount of chlorine or other problematic gases in the process the gas flow measurement is essential.
  5. Clinker cooler air balance: The clinker cooler is a central part of the process. The amount of enthalpy which enters the cooler as solid clinker versus the amount of enthalpy leaving the cooler via the process gas is a key parameter for the optimised operation of the clinker cooler.
  6. Stack: also on the stack a reliable and accurate measurement is needed. The swirl created by the ID fans is usually a challenge to any gas flow measurement.

A novel measurement is taking care of all the aforementioned problems in cement plants. The new measurement by PROMECON is a direct and digital measurement to determine the velocity of the process gas in the duct. This measurement is achieved by two sensors sensing the electric field of the particles in the process gas, which is passes by each antenna. The antennas are mounted at two different locations in line with the flow path of the gas.

The measurement determines the time of flight of the dust particles between the two sensors by digitally sampling the electric field of the gas and calculating the time lapse between the two sensors.

Any use of K factors or other proportional or non-linear corrections is not necessary in order to measure the gas velocity directly. Furthermore, a drift in amplitude of any of the raw signals will have no impact on the measurement result, as the algorithm of the system only calculates the time shift between the two raw signals looking at their pattern. The amplitude of these signals is not used to calculate any flow value, which is why this measurement will not react to any dirt or dust on the sensors themselves.

As the velocity measurement is purely based on time, it is not influenced by the density of the gas. This means that even at very high temperatures the velocity of the process, gas can be measured without any degradation in accuracy (gas temperatures of up to 1000°C are possible). Therefore, measurement of tertiary air or other hot combustion gases is not a problem. Furthermore, it must be noted that even slight abrasion on the antennas will not lead to any change in measurement accuracy as the slight change in sensor diameter or cross sectional shape will have no impact on the measured time delay between the two sensors.

The possibility to accurately measure gas flows in the cement making process opens up new ways to optimise the process itself in the following aspects:

  1. Reduction of fan power (a major source for energy consumption).
  2. Making the operation of the kiln more flat lined and hence less prone to quality problems with the clinker production.
  3. Lowering NOx by improving control of the calciner process through the tertiary air measurement and control.
  4. Better energy management in the clinker cooler by measurement of the enthalpy flows out of the clinker cooler.

In the world of thermal and industrial processes, PROMECON crosses new frontiers in the creation of accurate and reliable measurement systems, process data generation and plant optimisation.

  • We offer digital online flow measurement systems for novel applications in thermal and industrial measurement and control processes.
  • Our products explore the physical limits of accurate flow measurement for gas and solid mass flows in regards to temperature, flow dynamics or multiphase flow.
  • We enhance complex control loops in order to take process control to a higher degree of control quality.
  • We produce accurate digital measurement devices, which measure, collect and transmit process data, the raw material for enhanced process control of thermal and industrial processes.

Our measurement systems are key components for our clients in order to achieve better environmental compliance, lower energy consumption, reduce maintenance cost and increase operational safety.

Click here to watch a presentation on PROMECON's measurement systems and learn more about their solutions.

In addition, you can also watch PROMECON's spotlight interview with World Cement's Editor, David Bizley, as they discuss their latest article on how measurement technologies can be optimised to in order to achieve more 'green' cement production. Click here to watch the interview in full.

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