How to decrease costs for your daily operations by paying more attention to your liquor gun

You aim to decrease the costs of your daily operations? Pay more attention to your liquor gun! it is the key tool for keeping the reduction degree and, therefore, the costly makeup chemicals as well as emissions levels in the required range.

Special attention must be given to the recovery boiler and its operation, as it is the heart of each pulp mill. The liquor gun can be considered as the pacemaker of the boiler and triggers the main KPI of the boiler operation. Facing liquor gun errors may cause massive problems on the boiler and even a boiler stoppage. To prevent liquor gun errors in the future, we are researching and trailing with prototype liquor guns.

What are the errors and how Do they affect the boiler?

During our site visits and research activities, we have been faced with several problems at liquor guns. These errors mainly regard dissipated material and a loss of spraying pattern. The temperature, the pressure as well as the liquor properties, are causing high wears on bends and other temperature and pressure areas exposed to the gun. Moreover, there may occur problems concerning plugging of liquor guns if they are not cleaned regularly. The scaling inside the liquor guns is also an uncontrollable variable and must be checked on a regular basis. These problems may even cause a boiler stoppage, leading to significant production losses.

However, these erros can be prevented by properly cleaning the liquor guns from the inside and the outside, by using material with a higher wear resistance and by using different designs of liquor guns. Moreover, we have started to work on feasible solutions in order to prevent errors regarding liquor guns. The targeted results are lower maintenace and operating costs.

What is a recovery boiler?

A recovery boiler, often called soda recovery boiler or chemical recovery unit, is the heart of a pulp mill. It is responsible for making the Kraft process economical. It is recovering the process chemicals, which are used in pulping- and produces energy. For state of the art pulp mills, this energy is enough to cover their own need. The recovery boiler is the equipment with the highest operational- and asset costs. Furthermore, it presents the highest personal risk in the mill. Therefore, a careful handling of this equipment is required.

How is the boiler fired?

The boiler is fired with so-called “black liquor,” which contains the process chemicals as well the glue of the tree, the so called lignin. The black liquor is the product of the digester and is used to separate fibre from the wood. The process chemicals are mainly inorganic and, therefore, not combustible. The dissolved wood, however, is organic and, therefore, combustible.

The weak black liquor is evaporated from a low consistency to a concentration which is nowadays often above 75% dry solids. This strong black liquor is now pumped to the as fired liquor tank and afterwards, to the so-called liquor gun. The liquor gun is an instrument which serves as a burner for the black liquor and is therefore the most important part for combustion in the boiler.

What is the liquor gun and how does it work?

The liquor gun is an assembly which is mainly made of high alloyed stainless steel to sustain high temperatures und high ph of the black liquor.

There are several types of liquor guns as, for example, the splash plate gun and the beer can gun.

As an example we use the splash plate gun. It consists of a flange to connect it to the stand, a pipe which is guiding the liquor to the spoon and the spoon, also called splash plate, which is the part of the gun that is creating the spaying pattern. How the splash plate is forming the pattern is mainly influenced by the liquor properties as, for example, viscosity, temperature, pressure.

  1. Splash plate guns
  2. Beer can guns

The spaying pattern as well as the resulting droplet size is one of the main factors that influence how the combustion takes place in the recovery boiler. A good combustion is also a big influencing factor for the economy of the mill, due to the resulting recovery degree of the chemicals.

Which factors influence the spaying pattern when pressure and temperature of liquor are chosen right?

If the pressure and the temperature of the liquor are chosen correctly, the spaying pattern is mainly influenced by the cleanliness of the guns. Therefore, manual cleaning of the gun is required quite often. Modern boilers have installed liquor gun rodders, which are cleaning the gun automatically. However, these automatic rodding systems are only removing the coarse dirt on the liquor gun and don’t remove the dirt that is growing on the splash plate. This dirt is often looks like icicle which is growing on the splash plate and, therefore, destroying the spraying pattern completely.

What do we want to achive?

We want to prevent known errors in the future and provide the possibility to lower the maintenance as well the operational costs. Furthermore, a clear indication of the boiler operation can not only prevent future errors, but also increase the boiler lifetime. This service can translate into great possibilities to improve production volumes, lower the shuts or shut down times and, therefore, increase the turnover of the entire mill.

If you are facing one of these problems, you are cordially invited to reach out and discuss your case with one of our experts to increase the productivity of your mill and your production output!

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