Oil and Process Contamination

Contamination from oils, fats, and organic solvents may occur during food and beverage processing or similar operations. These materials inevitably find their way into the FW system, and from there to the boiler, unless adequate precautions are taken. 

Oily surfaces induce film boiling and the stabilization of steam bubble on the film surface, and overheating results. Oily surfaces also cause other problems, including  

Whatever the source of this type of contamination, it must be quickly and effectively removed from the boiler to prevent the problem from recurring. The standard procedure is to blow down the boiler to the maximum extent possible until the oil is removed. In more serious cases, it may be necessary to drop the boiler and provide a boil-out program. A boiler boil-out uses a simple formulation (usually based on caustic or strongly alkaline phosphates) and is employed to re-expose and repassivate the metal surfaces. 

Where oil in condensate cannot be eliminated at source, it should be removed by the use of an inline precoat filter. The precoating should be either aluminum hydroxide or ferric hydroxide because both these hydrous oxide gels have an affinity for oil. 

There are many process contaminants that may be inadvertently carried back with the condensate following either the purposeful injection of live steam into, say, an industrial manufacturing process or that can infiltrate the system due to a leaking heating coil, an open surge tank, or similar access point. 

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NOTE Oil and process contaminants may lead to steam-condensate system deposit problems in a fashion similar to entrainment. 

In recapping, DAF is the process of removing suspended solids, oils and other contaminants via the use of bubble flotation. Air is dissolved into the water, then mixed with the wastestream and released from solution while in intimate contact with the contaminants. Air bubbles form, saturated with air, mix with the wastewater influent and are injected into the DAF separation chamber. The dissolved air then comes out of solution, producing literally millions of microscopic bubbles. These bubbles attach themselves to the particulate matter and float then to the surface where they are mechanically skimmed and removed from the tank. Most systems are versatile enough to remove not only finely divided suspended solids, but fats, oils and grease (FOG). Typical wastes handled include various suspended... 

Contamination in this context refers specifically to the debasing of the purity of steam and condensate. Contamination may occur in the presence of unwanted steam volatile materials (such as silica volatiles), minerals carried over with BW, oil and process materials infiltrating the steam-water circuit, or by the results of corrosion processes. 

The major discharges from sulfuric acid alkylation are the spent caustics from the neutralization of hydrocarbon streams leaving the alkylation reactor. These wastewaters contain dissolved and suspended solids, sulfides, oils, and other contaminants. Water drawn off from the overhead accumulators contains varying amounts of oil, sulfides, and other contaminants, but is not a major source of waste. Most refineries process the waste sulfuric acid stream from the reactor to recover clean acids, use it to neutralize other waste streams, or sell it. 

Dispersant(s) or antifoulant(s) (sludge fluidizers, biodispersants, or mud treatments) to limit the physical adherence of insoluble salts, corrosion products, oils, fats, process contaminants, biofilms, and biomass onto heat-transfer and other water-wetted surfaces... 

Fig. 18.19. Fluid catalytic cracking—UOP LLC. Combustor style is used to crack process gas oils and moderately contaminated resids, while the two-stage unit is used for more contaminated oils. (Source Hydrocarbon Processing, 2004 Refining Process Handbook. CD-ROM. September 2004 copyright 2004 by Gulf Publishing Co., all rights reserved.)...

It transpired that the toxic oil was rapeseed oil that had been adulterated by the addition of 2 per cent of a chemical called aniline, as required by law in Spain for imported rapeseed oil so that it cannot be used for cooking. This oil had been refined and was sold for human consumption, as had been done before without adverse effects. It would appear that a batch of oil may have been refined differently or somehow became contaminated. The toxic oil was found to come from only one source within a particular refinery. The Spanish government agreed to replace the suspect oil with pure olive oil, after which the number of new cases subsided. Collection of contaminated oils known to be associated with the syndrome for analysis was a difficult task due to the government exchange programme. The results showed that the oil associated with the syndrome had a similar composition to rapeseed oil and contained contaminants as a result of the added aniline and the subsequent refining process. 

Dissolved air flotation (DAF) is the process of removing suspended solid, oils, and other contaminants via the use of air bubble flotation. Air is dissolved into water, mixed with the waste stream prior to being released from the solution and is in intimate contact with the contaminants. The small bubbles will attach to the floatable oils, increase their buoyancy, and reduce their specific gravity. In this system, a side stream of the oily waste is supersaturated under pressure with dissolved air so that the movement of the air bubbles will carry the floatables upward where they can be removed (46,51). 

The traditional methods of removing grease, oils, and other contaminants use an organic solvent to dissolve the contaminant. This is usually carried out by immersion into a hot or a cold liquid tank or by exposure to a vapor, thus producing a clean surface. However these processes are expensive and alterative methods have been employed using aqueous solutions of alkalies, which react with grease to form water-soluble salts (saponification). 

Removal of oil and hydrocarbon contaminations from recycled steam condensate for boiler feed water Reduction of total organic halogens and adsorbable organic halogens in industrial reserves of contaminated groundwater Process effluent treatment to meet the environmental legislation Removal of residual ozone and control of chloramine levels... 

Metals must be degreased as the first step in any metal preparation process, otherwise oil and grease contamination of blasting media, chemical treatments and machinery can result in severe factory quality problems and unreliable and variable bonding. 

The key to any contamination problem is to prevent it from happening. The cost of subsequent operations required to clean a product or rework a product is orders of magnitude more than any cost associated with preventing the contamination from occurring.These contaminants can cause soldering and solder mask or conformal coating problems. There are any number of possibihties for inducing contamination in an assembly environment, such as dirt, dust, machine oils, and process residues however, in many cases, contamination is caused by the human body, specifically the salts and oils on the skin. 

Surfactants are as important to the metal processing as to the mining industry. In order to perform as needed, metal surfaces must be cleaned and freed from deposits of oxides, oils, and other contaminants. Welding, painting, and other machining and surface treatments require a well-prepared surface. Even before that stage of... 

The gas processing options described in the previous section were designed primarily to meet on-site usage or evacuation specifications. Before delivery to the customer further processing would normally be carried out at dedicated gas processing plants, which may receive gas from many different gas and oil fields. Gas piped to such plants is normally treated to prevent liquid drop out under pipeline conditions (dew point control) but may still contain considerable volumes of natural gas liquids (NGL) and also contaminants. 

Petroleum and Natural Gas. Over 90% of the 428,000 t of caustic soda used in the petroleum and natural gas industry is used to process oil and gas into marketable products, especially by removing acidic contaminants. The remainder is used primarily to decrease corrosion of drilling equipment and to increase the solubiUty of drilling mud components by maintaining an alkaline pH (6). 

Common membrane processes include ultrafiltration (UF), reverse osmosis (RO), electro dialysis (ED), and electro dialysis reversal (EDR). These processes (with the exception of UF) remove most ions RO and UF systems also provide efficient removal of nonionized organics and particulates. Because UF membrane porosity is too large for ion rejection, the UF process is used to remove contaminants, such as oil and grease, and suspended soHds. 

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