Flow measurement in a brick factory when drying bricks

Measurements of exhaust air to regulate drying chambers in brick factories

Process data

Measuring task:
Flow velocity to determine flow rate

Measuring point:
Exhaust air of the chamber dryer

Measuring range:
Depending on the chimney’s diameter. For example in DN 1,100 mm from 10,000 – 90,000 m³/h

Process pressure:
Atmospheric, slight over or underpressure

Process environment:
Dusty, temperatures from 110 °C up to 180 °C max.
 

 

Your advantage

Safe
Safe, fast exhaust air flow rate measurement under all water saturation conditions, even with dust load and condensate.

Energy-saving
The measurement is part of the dryer regulation which helps save a lot of energy.     

Economical
Easy transfer of measuring data through the analog 4-20 mA signal and counting pulse. Very robust measuring method. Energetically viewing and optimising the drying process to save energy and reduce errors in drying by measuring flow rate of exhaust air.

Unique
This sensor with no moving parts allows measurements in dusty and condensate-laden brickworks exhaust air, within a wide measuring range from 0.5 – 40 m/s. Additional annular gap grouting is possible in case of strong condensation.

Addition
Design for all ATEX zones up to 180 °C with SIL2 or SIL3 certificate possible

Application

Brick drying happens in drying chambers that are fed with pallet trucks. The goal is to reduce any residual moisture to optimise the following burning process.

The drying process is often „regulated“ through simple temperature measurement and experience. To optimise this energy-intensive process the exhaust air‘s flow rate in combination with its water content need to be measured. This data is the foundation for process control. The bricks are being dried in the drying chamber until the desired residual moisture is achieved. The result of the brick factory‘s exhaust air measurement: an optimised use of energy while assuring quality. A measurement that pays off!

Recommended products

Up to 180 °C:
vortex flow sensor VA40 ZG7

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ATEX & up to 180 °C:
vortex flow sensor VA40 ZG8

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Up to 240 °C:
vortex flow sensor VA40 ZG4

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How is a brick made?

The brick has been used as building material since the new stone age. But how is a brick made? The manufacturing of bricks consists of several steps. Raw material is usually mud and clay in different compositions as well as added filling medium. The brick mass gets shaped, dried and then burned.

Brick drying and burning

Product dehydration and drying are part of the energetically intensive industrial processes. Up to 25% of the industry’s global energy consumption are required for these process steps. Fossil-fired exhaust air dryers are used in about 85 % of all drying processes. In 99 % of these systems the resulting water vapour is discharged with the exhaust air and (without measuring flow rate of the exhaust air) not further used energetically. Increasing efficiency of industrial drying processes is of great importance at the moment. Precise exhaust air measurement of hot, humid air is a requirement for significant energy and cost savings and therefore also an important factor in environmental protection. To exemplify the dimensions: a brick factory with a manufacturing output of 400 tons of burned bricks per day requires about 80 tons of water daily as mixing water content for the grouting brick mass – water that has to be driven out of the bricks and evaporated. An average energy requirement of 4000 kJ/kgH2O used for drying equals about 9000 m³ natural gas per day and is therefore the greatest loss of energy flow in brickworks (56. Würzburger Ziegellehrgang 2017).

 

Why is the drying process necessary for brick manufacturing?

After grouting the bricks they‘re dried in loads in the chamber dryer. The input moisture is usually about 21 – 23 %, partially up to 32 % residual moisture. Through the drying process which operates at about 100 °C a residual moisture of 1% is achieved.  This process is indirectly regulated by measuring brick factory exhaust air, since direct measurement of residual moisture in the brick is not possible. To monitor dryer exhaust air, a continuous measurement of the exhaust air’s flow rate is necessary. If the required level of moisture removal is not achieved it can cause cracks and breaks in the brick. The low moisture residue is necessary to avoid sudden vaporisation of the water at 800 °C to 1000 °C due to the high vapour pressure causing the bricks to „explode“.     

 

Status quo without flow rate sensor for hot exhaust air:

In general the temperature difference is compared to the heating diagram to adjust the process without measuring exhaust air from the chamber dryer. The problem: the moisture of the brick mass often varies. Sometimes it gets heated too much, too high or too low which leads to an increased use of energy or to defective goods.

 

How can energy be saved and product quality be ensured?

To improve energy use and therefore economical factors in brick drying, temperature and exhaust air flow rate need to be measured. With the measuring data of the dryer’s exhaust air the process in the chamber dryer is optimally regulated. By recording water content in combination with flow rate or the hot and dusty oven exhaust rate the drying speed and drying progress can be determined. These parameters ensure the continuous regulation of brick drying.

 

Flow velocity measurement in brick factories to ensure best quality

Even flow and temperature ratio in the drying chamber are the requirements for a nearly even drying time in the chamber dryer. Flow measurement of the brick factory’s hot exhaust air gives more insight into oven exhaust air’s flow conditions and into the regulation of fresh air supply. Flow measuring sensors for dust laden and hot air – such as oven exhaust air – deliver essential data to regulate the drying process and therefore the brick’s repeatability. Optimally regulated exhaust air flow rate and precise regulated temperature conditions help reduce the brick’s drying time in the chamber dryer. Essential: flow rate measurement of exhaust air prevents loss of quality in brick drying, like bending and cracking of the bricks. A shortened drying process also saves energy.

 

In what parts of the brick factory is flow rate of exhaust air / fresh air measured?

The process in the drying chamber is followed by burning the bricks in the oven. Starting temperature here is at about 250 °C to rise depending on the individual burning process up to 800 °C or even 1000 °C. Burning takes between 24 and 96 hours depending on the kind of brick. The hot and dusty flow rate of the oven exhaust air is energetically reused. The dryer’s exhaust air (mixed with fresh air) is refed to the chamber dryers making the drying process more gentle to the product and saving more energy. Additionally to the oven exhaust air in a brick factory also comes flow rate measurement of fresh air supply to flue gas afterburning to balance total exhaust air. Flow measurement in brick factories pays off for the company’s and the environment’s balance!