Pétrochimie

Innovative programmes for the petrochemical industry

Petrochemical production plants suffer from repeated operational disruption. Typical process-related problems are fouling, corrosion and foam problems. The consequences are high operating costs and occupational safety concerns. Our dedicated innovative treatment programs help to maximize performance, secure a failure-free operation of your plants and decisively contribute to a considerable reduction of the total operating costs.

Understanding your needs, goals and objectives are of great importance for us and our qualified experts will work with you on-site in order to meet the planned targets.

Besides the continuous further development of the conventional corrosion, deposit and polymerization inhibitors, Kurita primarily focuses on the development of innovative solutions to problems, such as:

  • Highly effective demulsifier programs to break stable emulsion phases
  • Innovative antioxidants and antipolymerants for quench water columns and process water stripper systems
  • Scavengers for mercury removal and elimination of red-oil fouling at caustic wash towers
  • Eco-friendly cleaning and decontamination additives
  • More effective defoamers (antifoams) for amine systems and stripper columns

Steam cracking of gaseous and liquid hydrocarbons is the leading technology for the production of ethylene. Naphtha, gas oil, unconverted oils or hydrocracker residues are typical liquid feed materials. Common gaseous feedstocks are ethane, propane and butane. In the presence of dilution steam, the feedstocks are routed to the steam cracker furnaces. The cracking furnace is the heart and starting point of the ethylene production. The gas-phase reaction is called steam cracking or pyrolysis. Steam cracking is a very complex process followed by cooling, compression and separation steps. Coking is an unwanted side reaction from steam cracking. It is a major operational problem in the radiant section of steam cracker furnaces and transfer line exchangers. Steam dilution lowers the hydrocarbon partial pressure of the cracked compounds. It favours the formation of primary reaction products. The steam addition reduces the tendency of coke deposition on the furnace tubes.

Coke is an undesired but inevitable side product of the pyrolysis. Surface catalysed reactions lead to the formation of filamentous coke. In many cases, the coke formation is caused by nickel and iron on the alloy surface. Amorphous coke is formed in the gas phase. Increased pressure drop, impaired heat transfer and higher fuel consumption cause high production losses. The external tube skin temperature continuously rises. This influences the process selectivity and leads to even more rapid coke formation. The formed coke has to be removed by controlled combustion with steam and air. It is a non-productive downtime of the steam cracker furnace.  Decoking cycles lead to shorter coil life of the steam cracker furnaces.

A continuous injection of a sulfiding agent is the historical method for coke reduction. DMS and DMDS are well-established additives. These sulfiding agents are believed to decompose to form sulfidic surfaces. This prevents coking and undesired chemical reactions. DMS and DMDS are very effective but have some drawbacks. Both sulfiding additives have a very bad smell and DMDS is commonly masked with odorants. It has a low flash point and requires special handling. DMDS is mainly used for steam cracking units. Storage under nitrogen pressure in closed containers is needed to avoid fire hazards.

Kurita has many years of experience with the supply and injection of polysulfides. Our polysulfides reduce the formation of undesired carbon monoxide (CO). It significantly extends the run time of the cracking furnaces. We supply DMDS but promote the use of another sulfiding agent, called CUT-COKE Technology. Kurita´s CUT-COKE is classified as non-hazardous and requires no special handling and storage. The high flash point of about 100°C reduces the risk of potential flash fires. The low sulfide odour is similar to gas oil. It does not have to be masked with odorants to cover up bad odours. Reduced material stress and low decoking times of the furnaces are further advantages of our chemical treatment.

Corrosion in petrochemical plants is an omnipresent thread. Many corrosive components are present in petrochemical process streams.  Hydrogen sulfide (H2S), hydrochloric acid (HCl) or hydrofluoric acid (HF) can be present in petrochemical feedstocks. Gaseous HCl and H2S are soluble in water and may cause severe corrosion. The hydrogen sulfide solubility increases with an increasing pH and decreasing temperature. Carbon dioxide or low molecular weight organic acids can be present in condensates.

Caustic is often used as a neutraliser for corrosion control but has significant drawbacks. Caustic can cause stress corrosion cracking (caustic embrittlement). Sodium salts can deposit and may accelerate fouling and polymerisation. Corrosion is an electrochemical process. It can be controlled through the use of a chemical corrosion inhibitor programme. For corrosion control neutralising amines, filming amines or oxygen scavenger programmes are applied.

The neutraliser must provide good corrosion protection when the first acidic droplets condense. Criteria for a good neutralising amine programme are its amine and amine salt properties. The amines have to provide excellent initial condensate protection. A low salt deposition potential and good pH buffering are required. Kurita´s alkalising amines operate by reacting with any acid constituent in a straight forward reaction.  The neutralising amine shifts the pH to a higher level, which improves the corrosion control. Our “ready-to-use formulations” provide the right combination of high-boiling and low-boiling amines. This ensures corrosion control in the steam and water phase.

Small amounts of oxygen accelerate corrosion when water condensation occurs. The metal surface reacts with oxygen by forming ferric hydroxide. The reaction product is insoluble in water and will precipitate. Corrosion by oxygen can be controlled with an oxygen scavenger. Oxygen corrosion is frequently observed in boilers or dilution steam generator systems (DSG). For many years hydrazine was used as a corrosion inhibitor. It is no longer allowed to be used in many countries being carcinogenic. Kurita´s very effective oxygen scavenger programmes are easy to handle. Our oxygen scavenger products are not carcinogenic in order to protect and maintain the health of the employees.

Kurita´s corrosion inhibitor filming programmes can help to stop or decelerate the corrosion. They will provide perfect protection by forming a very thin film. The film acts as a barrier against corrosive substances. If filming amines are selected, oxygen scavengers, phosphates and caustic dispersants are no longer required. The filming amines can be used in combination with alkalising amines.

We apply sodium-free corrosion inhibitor products. This avoids sodium-induced stress corrosion cracking and the formation of coke in the steam cracker. Dangerous amalgam corrosion in the raw gas flow is inhibited by the use of our special mercury scavengers.

Foam formation in petrochemical processes may lead to significant problems. It is a physical incorporation of gas bubbles within a liquid solution. Foam formation occurs at the gas-liquid interface. A low surface tension liquid allows the surface of a gas bubble to expand easily. Hydrocarbons, small particles and acids will increase the foam formation tendency and stability. Negative impacts of foaming are reduced throughputs, overhead losses and separation problems.

Affected are separation drums, distillation columns, extraction units or gas and liquid scrubbers. Acid gas scrubbers in ethylene plants are very prone to foaming. There foaming is often related to fouling problems. Solid polymer particles can stabilise the foam. Foam formation can increase the differential pressure. Negative effects are emulsions in the water wash section or unwanted salt carryover into downstream equipment. So foaming can become far more severe if polymerisation is a problem. Extractive distillations sections of butadiene recovery systems often suffer from foaming problems. Some foams show a very high stability. High film elasticity, high surface and bulk viscosity are foam stabilising factors. High solids content can also stabilise foams. They will accumulate at the liquid/gas interface. That prevents bubbles from coalescing and bubble rupture.

Immediate action is required to prevent or destabilize existing foams. Defoamers or antifoams are chemical programmes, used for foam control. Antifoams prevent the formation of foams. Defoamers destroy already formed gas bubbles.  A rupture of the film occurs because of a decrease of the surface area. This causes a large change in surface free energy. The result is the bursting of the bubble wall and is controlled by the “Marangoni Effect”.

Kurita´s antifoams or defoamers are surface active agents (surfactants). Our antifoams and defoamers meet the process requirements. Our highly efficient antifoams and defoamers destroy already existing foam immediately. A new formation of foam is prevented. Kurita ´s foam control programmes show rapid dispersion properties and chemical inertness. They have a lower surface tension than the foaming medium. Insolubility of the antifoam agent is very important for foam control. Our chemical programmes combine both functions to control foam formation. They have a very low solubility in the liquid solution. They enter the gas/liquid interface and concentrate at the surface film. This increases the elasticity of the liquid film on the gas bubble. Foam disruption forces allow the gas bubbles to rupture.

Kurita provides different types of foam control programmes. In petrochemical plants mainly silicone oils, organic or non-silicone antifoams are used.

To prevent these critical problems, Kurita offers phosphate- and polymer-based scale inhibitors. Potential scale-forming ions in the water are bound, dispersed and then removed from the boiler by blowdown. This prevents scale formation in the boiler and on the heating tubes.

Ethylene is mainly produced by stream cracking. This process includes thermal cracking, cooling, compression and separation. Hot cracked gases are immediately quenched in oil quench and water quench columns. The purpose of the cooling is to prevent polymerisation and formation of unwanted byproducts. The water quench column operates at low-pressure drop. The residual heat of the pyrolysis gas is recovered through absorption in hot quench water. In the oil/water separator, the hydrocarbons are removed from the quench water. The quench water from the oil/water separator is split with some being recirculated back to the water quench column.

Often the separated quench water still contains higher amounts of soluble and insoluble oils. Emulsification of hydrocarbons and water in the quench water can cause difficulties. Poor oil-water separation can result in sporadic loss of quench water. Negative impacts are level problems, fouling and corrosion of downstream equipment. Particularly affected are quench exchangers, the DSG system and process water stripper. Some plants install specially designed DOX units (Dispersed Oil Extractor). It is a skid-mounted system for oil-water separation. The emulsified oil and suspended solids are extracted from quench water. DOX units are designed to remove hydrocarbon concentrations down to 20 ppm or less. Emulsification problems may require a change out of DOX filter media.

A capable demulsifier programme can be applied to improve the separation of hydrocarbons and water. An overdose of the demulsifier should be avoided. The emulsion breaker additives have surfactant properties. They may have the tendency to act as an emulsifier at very high concentrations. A perfect demulsification can readily be recognised by visual inspection. Emulsified quench water´s appearance will vary from slightly hazy to milky/hazy.

In most cases, a demulsification of oil-in-water emulsions is required. Kurita provides high-performing demulsifier programmes. The hydrocarbons generally carry a negative charge at their surface. Hydrocarbons are steadily dispersed into small droplets because of their repellent forces. A cationic charged demulsifier programme neutralizes the negatively charged oil droplets. The repellent forces are weakened and oil droplets are brought together. The demulsifier resolves the emulsion of water and oil.   Our emulsion breaker additives accelerate the demulsification process. The oil-water separation involves three steps:

1. Agglomeration is the association of small dispersed phase droplets (clusters).

2. Creaming is the concentration of the dispersed phase.

3. Coalescence is the drainage of oil droplets, collected at the surface.

In petrochemical plants, there are many locations, where fouling is observed. Fouling deposits can come from contaminants in process streams or chemical reactions. They are the result of undesired oxidation, polymerisation, sedimentation and condensation processes. Reactive compounds are ethylene, acetylene, propylene, butadiene, styrene or other unsaturated components. Trace amounts of oxygen or oxygen-containing compounds promote the formation of gums and polymers. Fouling can be severe when monomers convert to polymers like the formation of „popcorn polymers“ from butadiene fouling. The most prevalent areas for polymerisation fouling are ethylene and styrene plants.

At high temperatures, the coking of hydrocarbons causes thermal fouling. Steam cracking furnaces mainly suffer from coke fouling. Heavy polynuclear aromatics (PNA) can precipitate onto the tube walls of the cracking furnaces. The PNA´s will dehydrogenate to form coke.  In petrochemical plants, the use of sulfur components is well established to control coke fouling. The injection of a sulfiding agent is the historical method for coke reduction. The sulfiding agent is typically applied to the dilution steam of steam cracker furnaces. DMS or DMDS are proven sulfiding agents for steam cracking operations. Both additives have several drawbacks. Kurita´s Cut Coke Technology is an alternative to that sulfiding products. We have many years of practical experience with the injection of polysulfides in petrochemical plants. Our polymeric sulfur formulation offers a safer and easier-to-use handling. It improves the run length of your cracking furnaces. This helps to increase your ethylene production.

Chemical fouling is caused by free radical polymerisation, Aldol condensation or Diels Alder condensation reactions. All these reactions can form insoluble fouling reaction products. Free radical polymerisation can happen at many different petrochemical processes. The most prevalent areas for polymerisation fouling are ethylene and styrene plants. The nature of the fouling deposits can be quite complex. To improve the ethylene production high-performing antifoulant programmes are required. The polymerisation can be controlled in the propagation and termination phase. Kurita´s antifoulant programmes terminate free radical reactions. They stop the chain transfer of hydrogen radicals or other reactive components. This will stop the polymerisation.

During ethylene production fouling in the raw gas, compression is an omnipresent thread. It reduces the performance of the cracked gas compressor and may lead to vibrations. Based on decades of experience Kurita developed a treatment concept, especially for raw gas compressors. The applied antioxidants and antipolymerants show excellent results. They do not cause a formation of hazardous nitrated dienes in the cold part of ethylene units.

Kurita adapts the antifoulant treatment concepts individually to your needs.  We combine the products and monitoring tools in compliance with your tasks and requirements:

  • Radical catchers (scavengers)
  • Dispersants
  • Oxygen scavengers
  • Stabilizers
  • Antioxidants
  • Metal deactivators

Pyrolysis of liquid and gaseous feedstocks for ethylene production is achieved in steam cracking units. The cracked gases contain carbon dioxide and hydrogen sulfide that must be removed from the cracked gas. Hydrogen sulfide is a catalyst poison for hydrogenation reactors. Carbon dioxide can freeze at low temperatures in heat exchangers and fractionation equipment. It can also be absorbed into ethylene, effecting the product quality and further processing. These acid gases are scrubbed with caustic solution (NaOH) in caustic wash towers. The caustic tower (caustic scrubber) is typically integrated upstream of the last compressor stage.

Caustic scrubber systems are frequently subject to polymer fouling. Fouling of the caustic scrubber internals and wet caustic oxidiser are known problems. They are recognised by the operators as “Red-tide fouling” or “Red oil”. Sodium carryover to the next compressor stage is not unusual and leads to problems with the downstream units. Aldol condensation products and high concentrations of C4 and C5 diolefins are formed. Aldol condensation polymerisation is a base catalysed reaction. The cracked gas contains carbonyls like aldehydes and ketones. The presence of acetaldehyde in cracked gas streams is quite common.

The caustic base removes a proton from the aldehyde molecule by forming a carbanion. This carbanion will react with another aldehyde molecule to form the aldol group. It still contains a reactive aldehyde that may continue to react. The polymers create longer chain lengths in the caustic scrubber and remain suspended in the caustic solution. Aldol condensation products are often called “Red Oil” because of the orange to red or brown-red colour. The polymers can absorb other organic materials from cracked gas. This will increase the pressure drop and fouling formation. Additionally, unsaturated compounds such as 1,3 butadiene can be easily dissolved in caustic solution. Together with metal oxides and oxygenated compounds, more polymers are formed to increase the red oil production.

Kurita has developed high-performing antifouling concepts which inhibit the aldol condensation. Formation of red oil polymer materials will be avoided. Antifoulants with dispersant properties keep the polymer particles small enough to avoid agglomeration of the polymers. Antifoulants with radical catcher properties will stop the free radical polymerisation mechanism. The treatment programme can be monitored by analysing the spent caustic. Successful treatment will lead to the elimination of expensive gasoline wash. It will reduce the load on the spent caustic oxidation unit. This will reduce COD load on the wastewater plant. A sodium contamination in the DSG system through recycling of the spent gasoline will be avoided.

Oil refineries and petrochemical plants operate with quite a large number of different distillation equipment. That are columns, knock-out vessels, distillation columns, heat exchangers and pipe systems. Fouling is an omnipresent problem. The drawbacks of fouling are throughput reduction, significant losses in energy recovery or generating an increase in pressure drop of distillation columns or heat exchangers. Periodical cleaning and decontamination is mandatory and the equipment needs to be checked for maintenance or repair.

A planned shutdown is a very labour-intensive time, which often requires several weeks of downtime. Heavy fuel oils, greases, tars or tenacious fouling materials must be removed. Contaminated tanks, columns, heat exchangers or pipelines have to be drained for cleaning and degassing. Fouling deposits may contain hazardous components and harmful gases. Toxic hydrogen sulfide, volatile hydrocarbons or carcinogenic benzene can be released. Iron sulfide (FeS) easily accumulates in pipes, trays, structured packings, heat exchangers and vessels. Due to its pyrophoric nature, it can become a serious problem. Iron sulfide has a high potential for spontaneous auto-ignition. It oxidizes exothermally when in contact with air. Most FeS induced fires occur during shutdowns when the equipment is opened for maintenance and inspection.

Healthcare, safety and environmental protection are very important aspects. Personnel in charge is requested to minimise exposure of workers to any situations, where auto-ignition of iron sulfide species or health risks could be initiated. Contact with decontaminated materials should be avoided. The removal of benzene, pyrophoric iron sulfide, toxic hydrogen sulfide and other hazardous gases is absolutely necessary for safe working conditions. The adherence of the lower explosion limit (LEL) has to be achieved.

Kurita provides a wide range of various products such as cleaning chemicals, degassing agents or combinations thereof. The handling of our cleaning and decontamination additives is easy and safe for the operating personnel. High-performing chemical cleaning agents with tailor-made cleaning and degassing methods are used in order to reliably achieve these targets. Cleaning and degassing of distillation columns and vessels can be done with excellent results within one day. Removal of heavy fuel oils, tars, greases and other tenacious materials are key elements of the cleaning. The complete elimination of hazardous gases and fire potential risks have great importance. Cleaning of the metal surface without attacking the distillation equipment is a matter of fact.

Heat recovery is essential in process units which are operated with reactors. Mechanical cleaning of complex heat exchanger networks can take several days and inaccessible areas cannot be reached. By comparison, Kurita´s cleaning and degassing solutions reach inaccessible areas. The cleaning can be done in situ within one day. Less labour intensive work compared to mechanical cleaning will be required. Tailor-made chemical cleaning programmes from the Kurita CD series are used when very efficient cleaning results are needed. Packinox plate heat exchangers or Texas Tower tubular heat exchangers require more cleaning efforts than classical heat exchangers. Kurita´s cleaning concepts are the method of choice when Packinox heat exchangers or Texas Towers need to be cleaned.

A mechanical cleaning and decontamination of storage tanks may require several weeks of downtime. In comparison, the chemical cleaning and degassing will reduce the downtime significantly to a few days providing a great economic advantage.

Kurita provides you with cleaning and degassing programs customised to your needs. Our trained staff will support you in your cleaning and degassing processes. Upon request, we supply the related equipment.