Equipment Cleaning Technology
Water used in heating and water supply systems contains calcium, magnesium salts, iron oxides, and various solid particles. In addition, bacteria secreting waste products are constantly present in the water. Also, various contaminants because of lubricants, entry of contaminants into pipe defects, non-compliance with the installation requirements and poor cleaning lead together to the formation of scale, solid deposits and mucus on the inner surfaces of pipes and equipment. Thus, the pipe inner diameter and the flow area size are reduced. In addition, the automatic equipment of the heating and water supply system is depressurized.
All solid deposits are formed during crystallization. In heating systems, salt crystallization occurs with increasing temperature.
Let us consider the classification of solid deposits:
- complex silicate;
Alkaline-earth deposits include carbonate, sulfate, silicate, phosphate scales.
Carbonate scale – CaCO3 – is deposited in the shape of dense crystalline deposits on those heating or cooling surfaces with no boiling of water and with a non-alkaline medium (water economizers, turbine condensers, water heaters, heating networks).
Sulphate scale – CaSO4 – is usually very hard and has a high density.
Silicate deposits include complex silicate scales with different mineralogical composition. Silicate scales are quite diverse – from porous and lumpy deposits to hard and dense formations.
Iron scales include:
Iron phosphate scales. This type of scale is formed at low water alkalinity and high iron content and is deposited on the inner surfaces of the steam-generating pipes. They are a loose residual coating.
Iron-acid scales are deposited in a continuous layer or in the shape of flakes.
Fourth Group. This Group includes deposits of copper/ They are formed with an increased content of copper in water in steam-generating pipes with a high heat load. They are deposited in the shape of layered formations.
So, for example, during boiler operation, with changes in its hydrodynamic and thermal regimes associated with an increase in the load, temporary sodium deposits (Na2SO4, Na2SiO3, NaCl) may form on the walls of the wall tubes. Being well soluble in water, such deposits are completely washed out from the walls of the boiler tubes when its stop or after a sharp decrease in load.
ASGARD-Service Company is engaged in cleaning and maintenance of engineering systems, heat exchangers and boilers from all types of deposits.
Let us consider in more detail the methods of cleaning equipment and the procedures used by the ASGARD-Service Company.
Before choosing a cleaning method, our specialists go to the site to examine and inspect engineering systems.
- Samples of deposits are taken to select a reagent and a cleaning method.
- They request technical documentation for complete information on the material and age of engineering systems.
After that, the optimal method for cleaning the equipment is selected:
- chemical washing;
- hydropneumatic washing;
- combined method
It is used for cleaning heating systems, heat exchangers (both collapsible and non-collapsible) and boilers. For washing, a 10% solution of acids is used – hydrochloric, orthophosphoric or formic one. Cleaning is carried out with a change in the direction of circulation of acids or reagents; this makes it possible to carry out better cleaning.
Today, Asgard-Service specialists prefer to use patented detergents improving the washing process, dealing with deposits better and protecting the inner surfaces of pipes against corrosion.
If the washing was carried out with acids, then our specialists necessarily use passivating solutions after washing to prevent corrosion.
Washing is carried out using specialized equipment – a chemically resistant pump, hoses resistant to alkali and acid solutions as well as specialized CIPs. Now, Asgard Service Company uses its own CIPs.
CIP advantages are obvious:
- easy to use saving work time and labor costs
- efficient washing
- cost effective – it is better to carry out preventive cleaning of equipment before the heating season than to spend money on its expensive repairs and emergency shutdown.
For the process efficiency, it is possible to heat the washing liquid to improve and speed up the process. After washing, the spent reagent is neutralized with an alkali solution to a neutral pH and drained or disposed.
Further, the specialists of our Company carry out pressure testing of the system including injecting pressure into the system by 1.5 atm. more than operating one to check the system performance and identify leaks.
A portion of compressed air is supplied to the system under high pressure with the help of a compressor; as a result, the fluid flow rate in the system increases several time leading to mechanical detachment of near-wall pipe deposits together with the oscillatory movements of the compressed air. Deposits are removed from the system through a discharge point.
Now, our Company has developed and patented the PnIU-200 special installation for hydropneumatic washing. The approximate scheme of PnIU-200 operation is as follows: a certain amount of compressed air or nitrogen is pumped into PnIU-200 (nitrogen is used for no chemical reactions in the system), then the PnIU-200 unit is connected to the system being washed; when the unit valve is opened, a fast gas supply under pressure from PnIU- 200 is performed into the system resulting in wave vibrations developed in the liquid in the pipeline; this process contributes to the detachment of scale and other near-wall deposits in the pipeline removing them through the discharge point after it. Washing by the pulse-wave method is performed until clean water begins to flow into the drain tank. That is a criterion for high-quality cleaning.
The photo shows the connection scheme of the air gun to the heating system.
The advantages of our development are obvious:
- This cleaning type is safe.
- Reducing the washing time and improving its quality.
- Washing is performed without any chemicals reducing cost of work.
This installation uses the so-called “pneumatic explosion” method.
Next, the system pressure check is performed.
It is a combination of chemical and hydropneumatic washing. The technologies used in this method are described above.
In addition, an important aspect of work for our Company is the cleaning of oil pipelines as well as tanks for storing oil against heavy fractions of hydrocarbons.
In the process of work on the in-wall space of technological equipment and oil pipelines, a sediment of asphalt-resin-paraffin deposits (hereinafter – ARPD) is formed.
The deposit is a mixture of heavy oil components: paraffin-naphthenic hydrocarbons, resinous-asphaltene substances, mechanical impurities and particles of bound oil. Asphalt-resin-paraffin deposits settle on the metal surfaces of the equipment, impede the extraction and transportation of oil and make further operation of the equipment impossible.
The cleaning technology is as follows
- displacement of oil from oil pipelines;
- preparation of main and auxiliary oil pipelines and equipment surface;
- pumping of ARPD solvent through main and auxiliary oil pipelines;
- pumping ADT to remove residual ARPD solvent from the internal surfaces of the oil pipeline;
- pumping of CDT to assess the quality of cleaning the inner surface of oil pipelines and equipment.
After oil was displaced from the section of the system being washed, ASGARD Service experts injected a specialized ARPD inhibitor approved by the Transneft Research Institute into it.
Then the inhibitor was in a static state in the system, following that, it was circulated in different directions.
Next, the inhibitor was removed and disposed and diesel fuel was filled in it instead: 2 batch of adsorption and one control lot, for quality control.
The time of draining and filling a new batch of diesel fuel was determined by sampling checked in a specialized laboratory for sulfur.
To improve the quality of cleaning, Asgard Service Company’s experts heated up the ARPD inhibitor.
Since these works were carried out with hazardous substances, the equipment had to comply with all safety measures, and therefore the experts of our Company used specialized and highly targeted equipment, for example, explosion-proof pumps and stainless steel hoses with titanium threads.
In addition, all employees were equipped with personal protective equipment and portable gas detectors.
It should be noted that the engineers of our Company are constantly conducting research and development work in this direction developing equipment for better washing of oil pipelines. Now, an internal pipe circulation piston has been developed and patented for cleaning the inner surface of pipelines and oil pipelines.