Liquor gun: A dangerous cost driver for recovery boiler maintenance but doing it right key for a sustainable and cost-effective pulp mill run

You have to keep costs for your daily operation down? Pay more attention to your liquor gun: it is the key tool to keep the reduction degree and therefore the costly makeup chemicals as well as emissions levels in the required range.

Special attention must be keep on recovery boiler and its operation, which is the heart of each pulp mill. The liquor gun is 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 future we are researching and trailing with prototype liquor guns.

What are the errors and how they are affecting the boiler?

We are faced with several problems at liquor guns during our site visits and research activities. Mainly there are errors with dissipated material and a loss of spraying pattern. The temperature, pressure as well as the liquor properties, is causing high wears on bends and other temperature and pressure areas exposed of the gun. Further on there are problems with plugging of the liquor guns, if there are not cleaned constantly. The scaling inside the liquor guns is also a uncontrollable variable and must be checked constantly. All these problems can even cause a boiler stoppage event and lead to production losses.

Also massive problems with spoon burning are faced off in several mills. This error is a big problem, due to total loss of spraying pattern and massive grow of char bed.

These erros can be prevented by propper cleaning of the liquor guns from inside and outside or by using better material which is showing higher wear resitance. Also different designs of liquor guns can be used to prevent this problems. Therefore we started to work on feasible solutions to prevent them. The targeted result will be 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 to make the Kraft process economical. It is recovering the process chemical which are used in pulping- and produces energy. For up to date pulp mills this energy is enough to cover their own need. The recovery boiler is the equipment with the highest operational as well as high asset costs. Further, it has highest personal risk in the mill. Therefore, a careful handling of this equipment is required.

How the boiler is 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 digester to separate fibre from the wood. The process chemicals are mainly inorganic and therefore not combustible on other hand the dissolved wood 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 after 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 it is working?

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 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 how 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 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 the resulting recovery degree of the chemicals.

What is influencing the spaying pattern when pressure and temperature of liquor are chosen right?

If pressure and temperature of liquor are chosen right 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. But often this automatic rodding systems are only removing the coarse dirt on the liquor gun and don’t remove the dirt which is growing on the splash plate. This dirt is often looking like icicle which are growing on the splash plate and therefore destroying the spraying pattern totally.

What do we want to achive?

We want to prevent known errors in the future and give the clear possibility to lower the maintenance as well the operational costs. Further a clear indication of boiler operation can be given to prevent future errors as well stretch boiler life time. This service can give huge 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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