Energy and production management in relation to cleaning

Fouling

Fouling has a negative effect on the operation of process equipment. It is a phenomenon that occurs in many natural, domestic and industrial processes. The type and composition of the fouling is related to the type of process and the type of equipment. Reduced flow, pressure and heat transfer or corrosion are indicators of increased fouling of process equipment. In practice, there appears to be more than one type of fouling, e.g.: inorganic scaling, corrosion products, dirt, sand, organic growth and organic deposits. Deposits vary from very sticky to thick layers of various hardnesses. These layers are categorized as general fouling where suspended particles are deposited on the surface. The speed of deposition is proportional to the particle size and inversely proportional to the viscosity and density. These deposits are, normally speaking, soft and easy to remove. This general form is called sludge.
Other deposits include:
Scaling: this is a form of crystallization. This phenomenon mainly relates to high concentrations of insoluble salts in cooling water, which deposit on the heat-exchanging surface as a consequence of increasing temperatures. Sulphide or oxide layers that are formed by high-temperature corrosion can also cause scaling.

Sendimentation: this is the deposition of fine mixed solids, which are carried in the process fluid, such as rust particles, clay, etc. Polymerisation: this refers to deposition caused by chemical reactions where the surface material is not involved (oil oxidation and polymerisation products).

Cokes: this is a hard crust deposition of carbohydrates, usually formed at high temperatures.

Oragnic growth: this concerns macro-biological growth such as algal growth.

Corrosion: where the fouling is caused by the accumulation of corrosion products on the heatexchanging surface.

Fouling abatement

In the past, installations were more frequently inspected and bundles had to be removed and cleaned for inspection. Now an inspection interval is determined based on a Risk Based Inspection and bundles do not have to be inspected as frequently. Consequently, one is more influenced by the degree of fouling than by the inspection intervals, and bundles can be left untouched to be cleaned in-line. The advantages of this are: less risk of damage, less waste and shorter stoppages.

Operational availability versus profit

The fouling of process installations as a consequence of given process conditions means a reduction in production capacity and operational availability. Necessary maintenance and cleaning work are the result. Moreover, fouling is responsible for substantially higher energy consumption and maintenance costs as well as having a greater impact on the environment and higher emissions. One of the most important topics nowadays is operational availability. Every hour that, for example, a refinery can cost-efficiently and energy-efficiently produce without stoppage is extremely important for the refinery profit, the so-called “Gross Refinery Margin”.

Energy saving

The strong increase in interest for saving energy and the demand for increasingly higher plant availability make the subject of fouling not only more interesting but also more difficult. The wish to sace energy results in significantly smaller temperature differences between hot and cold media and consequently to substantially larger heat exchange surfaces.

Efficiency of processes

Increasing energy prices have meant that the efficiency of processes in general and of plant machinery such as heat exchangers in particular has become increasingly more important. To save energy, the heat-exchanging surface, which is now used in certain installations, has been increased substantially compared with similar installations of, for example, 10 years ago. The strongly increased energy prices emphasise the importance of better insight into the phenomenon of fouling.

Financial importance

The financial importance of fouling can be best indicated by the annual costs associated with the contamination of the process installations in industrial processes, namely approximately 0.3% of the Gross National Product.

The costs resulting from fouling can be attributed to:

- additional charges on fixed assets, as an extra surface is installed in the heat exchanger to compensate for the increased heat resistance;

- loss in production, as contamination reduces production capacity and operational availability. In the end, production must be halted to clean the installation;

- energy loss caused by narrowing passages as a result of fouling and therefore higher process medium flow rates which results in higher pressure losses; contamination can mean that less heat is exchanged, such that more heat or energy must be pumped into the system via, for example, the furnace.

Fouling costs

For a hypothetical refinery, the fouling costs comprise approximately 50% for the reduction in the throughflow of product, 49% for extra energy and 1% for maintenance and cleaning. These figures give an indication of where the costs lie in this important industry. The alternative is to use tailored and efficient inline/online cleaning methods. Altena Industrial Services BV is constantly looking for efficient and safe techniques to take stock, prepare and clean industrial processes and installations using new methods. These techniques include insitu online cleaning/ decontamination of process installations without disassembly using mobile facilities and a front-end approach, including limiting waste flows and aided by specialist support using “factbased monitoring”. The most suitable approach and especially developed non-corrosive cleaning agents are employed here. They can be fully homogenised in the rinse medium to be used in “a one step approach”. The result for you is that the operational availability and integrity of your process installation is substantially increased.

Crude fouling

For years, cleaning crude fouling in installations has been a time-consuming and expensive business. Equipment fouled with crude fouling can be cleaned using in-line circulation. Besides removing the fouling, one can also remove H2S such that the installation can be immediately handed over gas-free. The resulting quantity of wastewater is substantially less than cleaning with conventional methods and easy to separate. By using the right chemicals, one can make the thickened crude pumpable again. These chemicals are not water but oil-soluble, which means that the waste, which is produced after filtering, can be returned to the process.