Air Purification In Refinery & Petrochemical Plant

BryairArticlesAir Purification In Refinery & Petrochemical Plant

The industry tends toward both vertically and horizontally integrated operations. Vertical integration in the industry is typified by petroleum refiners using their hydrocarbons to produce primary and intermediate petrochemical materials and subsequently converting them to such products as plastics, synthetic fibres and synthetic rubber. Horizontal integration is apparent in firms that manufacture a family of related petrochemicals of similar types or for similar markets. Plastic products, fertilizer materials and surfactants are examples of groups of related products.

This industry was one of the first to go for computerization of its process controlled applications, and one of the first to see the need for corrosion control of those electronic process controls.

Creation of Contaminant Gases

The processes involved in the petrochemical production area generate sufficient quantities of hydrogen sulphide, sulphur dioxide, and nitrogen oxide, other than many high molecular weight hydrocarbons. Chlorine and ammonia too are present in small concentrations. These hostile gases are ever present in these environments with their average outside ambient levels between 0.5 to 1 PPM.

Areas needing air purification equipment

The following locations are prime application areas for air purification equipment to protect electronic equipment housed in the various control rooms and switchgear rooms:
Distillation
Catalytic Cracking
De-sulphurization
Coke plant
Oil by-products
Tank farm
Oil loading / handling areas
Power generation plant

Air Purification methods for Petrochemical Plants

For controlling gaseous contaminants infiltrating in the Control/MCC rooms from outside air
Two types of solutions are available for control and elimination of contaminants, depending on the size and frequency of pedestrian traffic of the room. They are as follows:

In case of rooms with very low movement of personnel coming in and out, only pressurization with chemically cleaned air is sufficient.
Provide from 3 to 6 air changes per hour, to attain approximately 2.5 to 5 mm WC positive pressure inside the room. By this method, there will be a net outflow of clean air from inside the room to outside atmosphere only, thereby eliminating the leakage of outside contaminated air into the room.
Mostly, all centralized Computer/Control rooms, Rack rooms and MCC locations would require this type of air purification.

Rooms with high pedestrian traffic, such as, Operator Control rooms would require air purification by re-circulation mode in addition to air pressurization. This is due to the absorption of contaminants on clothes and body surface of plant personnel while attending to duties at the different process locations, which are generally highly contaminated. Such absorbed gases would immediately de-sorb upon entry to a relatively cleaner area.

For such areas, it is advisable to provide re-circulation type air purifiers working independently, in addition to the pressurization equipment. The equipment should be designed to handle 6 to 10 air treatment cycles or air changes per hour, wherein the inside room air is continuously cleaned of contaminants that are being carried in due to movement of personnel. The pressurization equipment here, should provide 3 to 6 air changes per hour, as already explained above.

However, in view of the extremely critical process parameters in a petrochemical facility, wherein even a small malfunction can cause tremendous loss in revenues, it is strongly advised to use both pressurization as well as re-circulation scrubbers in all the protected locations.

Typical media to be used in the pressurization scrubbers would be one bed each of:
plain activated carbon media (for HCs like toluene, benzene etc., chlorine, nitrogen dioxide)

caustic impregnated activated carbon-alumina media (for high concentrations of hydrogen sulphide, sulphur dioxide & chlorine)
potassium permanganate impregnated activated alumina (for NOx, mercaptans, low concentrations of acid gases).

The media beds are to be placed in the same order as mentioned – the first bed being of plain activated carbon to face the contaminated air at scrubber inlet.
In many a cases, potassium permanganate impregnated activated alumina media can be dispensed with in the third bed, and caustic impregnated activated carbon-alumina can be used in it’s place.

In locations having ammonia contamination eg. de-waxing area, the second bed should be of acid impregnated activated carbon.
In-room re-circulation scrubbers should have one thin bed of plain activated carbon and another thin bed of potassium permanganate impregnated activated alumina media.

Other important design requirements

Room Air-conditioning
Less than 50% Relative Humidity with less than 6% change per hour.
21-23°C, with less than 1°C change.

Room Construction & Integrity
Well Sealed Room (not leak-proof – small amount of leakage is desired and is a requirement).
Provision of airlock entryways, with door/ windows provided with weather-stripping.

** Important: Due to flammability concerns of virgin Activated carbons in a refinery environment, the particular media is essentially given as a 50-50 blend with potassium permanganate impregnated activated alumina.

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