Introduction to Process Technology

Lesson 3

Safety Topic | Gas Processing Methods| Basic Terms

Objectives

1. Describe gas plant processing fundamentals.

2. Describe Gas Processing methods

3. Describe Gas Treatment Processes:

4. Describe Product Treatment

5. Describe Petrochemicals

6. Describe Plastics

7. Basic terms of Maintenance Operations and System Components:

8. Basic Math Continued:

Safety Topic

Today's safety topic is Hazard Recognition. All around you every day, hazards exist. They may take the form of a speeding truck, or an ice covered sidewalk. Here are some categories of hazards:

Slipping
Crushing
Chemical
Tripping
Falling
Burning
Electrical
Mechanical

In a process operation environment, much thought goes into minimizing the possibility of injury caused by these hazards, but it is not possible to completely eliminate all hazards. As an employee you are the person most concerned with your personal safety, and as such you must be able to identify, and protect yourself from hazards.

Gas Processing Methods

Gas must be treated before it can be sent on to the final customer. Three primary methods of treating gas are adsorption, absorption and catalysts. These methods are performed in closed process equipment.

Absorption is the disappearance of one substance into another so that the absorbed substance loses its identifying characteristics, while the absorbing substance retains most of its original physical aspects. Used in refining to selectively remove specific components from process streams. One simple absorption process, which is also very common, is the use of glycol to absorb water from gas.

Adsorption is the adhesion of the molecules of gases or liquids to the surface of solids, as opposed to absorption, in which the molecules actually enter the absorbing medium (see adhesion and cohesion). Certain solids have the power to adsorb great quantities of gases. Charcoal, for example, which has a great surface area because of its porous nature, adsorbs large volumes of gases, including most of the poisonous ones, and is therefore used in gas masks. Certain finely divided solids have great adsorptive properties; for example, minute particles of platinum attract and hold multitudes of hydrogen molecules on their surfaces. Its ability to adsorb other gases makes platinum very useful in the production of sulfuric acid by the contact process and in the preparation of ammonia.

Definitions

Dry Gas: Natural gas with so little natural gas liquids that it is nearly all methane
Sour Gas :Natural gas that contains corrosive, sulfur bearing compounds such as hydrogen sulfide and mercaptans.
Fuel Gas :Refinery gas used for heating
Desulfurization :a process in which the principal purpose is to remove sulfur from gas.
Knockout Drum :A vessel wherein suspended liquid is separated from gas or vapor Hydrogen Sulfide

Dehydration or drying of gas is accomplished by the use of water absorption or adsorption agents to remove water from the gas.

Look at slides 3-2 and 3-3 for a simple system.

The wet gas is sent to the glycol contactor. The contactor is a drum filled with trays or a mesh to maximize the mixing of its input products. Glycol is a liquid with a great affinity for water. Glycol does not absorb natural gas.

The glycol is pumped into the upper section of the contactor drum where it cascades down the inside of the drum coming into contact with the gas, which is bubbling upward. At this point the glycol absorbs any water that is in the gas. The dry gas goes out the top and the liquid glycol, now combined with water, goes out the bottom. The glycol is regenerated and then sent to the contactor drum again.

Not all of the glycol goes out the bottom on the contactor. A small mist of glycol will go out the top with the gas. Therefore a glycol knockout drum is used to get the last of the glycol out of the stream.

Desulfurization: Sour gases are dried and sweetened. Sweetening removes sulfur and also reduces concentrations of carbon dioxide.

Note, this section is about recovering sulfur from natural gas, keep in mind that sulfur is also removed from liquids.

Sulfur Recovery from hydrogen sulfide. Sulfur recovery converts hydrogen sulfide in sour gases and hydrocarbon streams to elemental sulfur. The most widely used recovery system is the Claus process, which uses both thermal and catalytic-conversion reactions. Sulfur is separated from natural gas as hydrogen sulfide and then converted to elemental sulfur by the Claus process, which involves the partial burning of hydrogen sulfide to sulfur dioxide

Hydrogen sulfide or h2s is an extremely toxic gas that smells like rotten eggs. It commonly occurs in natural gas and must be removed.

First, the hydrogen sulfide is absorbed from the natural gas at ambient temperature in a scrubber, either in alkanolamine-glycol solution or in aqueous alkaline carbonate solution. This scrubber works much like the glycol concentrator mentioned above/

Second, the hydrogen sulfide is partially oxidized to SO2 with considerable evolution of heat:

Third, this resulting sulfur dioxide is then reacted with hydrogen sulfide in the presence of Fe2O3 as a catalyst to yield the more conveniently handled elemental sulfur:

Removal of free sulfur: Sulfur also occurs in natural gas as a free element. This material is removed in a vessel by running the gas through an aluminum sieve. The free sulfur will adsorb on the aluminum. The aluminum then catalyzes or burns the sulfur to eliminate it. In cases of large amounts the sulfur is recovered and sold as a marketable by product.

Product Treatment

Many petroleum products take their final form only after substantial treatment. The first stage of treatment extracts the feedstock from the crude. Subsequent treatment includes both processing by specialized equipment and the mixing in of special substances. Two products in which we we go into some detail are lubricating oils and petrochemicals

Lubricating Oils

Lubricating oil base stock is "cut" from the crude stream but must be processed to give it properties needed in modern engines. These properties include the ability to withstand extreme temperature ranges without changing its viscosity (properties of lubrication). To give the motor oil needed properties the following additives are used

Demulsifiers An additive that promotes oil-water separation in lubricants that are exposed to water or steam.

Antioxidants All petroleum products are subject to oxidation, with resultant degradation of their composition and performance. Antioxidants bind the free oxygen in the oil and hold it until the next oil change.

Viscosity improvers A lubricant additive, usually a high molecular-weight polymer, that reduces the tendency of an oil to change viscosity with temperature.

Emulsifier. An additive that promotes the rapid mixing of oil and water to form a stable emulsion. Emulsifiers are sometimes used in motor oils to allow water, formed by combustion of fuel, to be kept in emulsion until engine heat can evaporate it. Emulsifiers are also used in soluble oils used in some metal working operations and in some fire resistant hydraulic fluids. Emulsification is not a desirable property in most hydraulic fluids or turbine oils.

Corrosion and Rust Inhibitors. Rust inhibitors protect ferrous (iron or steel) parts by forming a film on the part that resists attack by water. Corrosion inhibitors act in a similar way to protect nonferrous parts and also act to neutralize acids with a basic compound such as calcium carbonate.

Petrochemicals

Many products derived from crude oil refining, such as ethylene, propylene, butylenes, and isobutylene, are primarily intended for use as petrochemical feedstock in the production of plastics, synthetic fibers, synthetic rubbers, and other products.

Plastic is a common name for Polymers: materials made of long strings of carbon and other elements. Each unit in a string is called a monomer, and is a chemical usually derived from oil. The monomer is made into polymer by chain-linking reactions. This is like making a daisy chain. Instead of flowers, carbon atoms are joined together. The appearance of the daisy chain will be different if you use different colored flowers, and so will polymers.

There are many different types of plastic, depending on the starting monomer selected, the length of polymer chains, and the type of modifying compounds added. Each plastic has been developed for a special purpose. For example ethylene is polymerized to produce the plastic polyethylene.

The plastic PVC is formed by combining pure chlorine and ethylene (obtained by cracking natural gas). The result is ethylene dichloride, which is then used to make PVC compounds.

Vinyl

Vinyl results from a series of processing steps that convert hydrocarbon-based raw materials (petroleum, natural gas or coal) into unique synthetic products called polymers.

The other half of the vinyl polymer is based on the natural element chlorine. Chlorine gives vinyl two advantages.

First, chlorine is derived from brine -- a solution of common salt and water, and a readily available, inexpensive commodity. Thus, vinyl is less sensitive to fluctuations in the world oil market than are totally oil dependent polymers.

Second, chlorine has excellent inherent flame retardant properties. These properties are passed on directly to vinyl end products, making vinyl an excellent choice for applications such as electrical conduit and wiring that require high resistance to ignition and flame spread.

Through a chemical reaction, ethylene and chlorine combine to form ethylene dichloride, which, in turn, is transformed into a gas called vinyl chloride monomer (VCM).

A final step, called "polymerization," converts the monomer into vinyl polymer, a fine-grained, white powder or resin known as polyvinyl chloride (PVC), or simply "vinyl."

Vinyl resin, however, is still one step away from being a usable material: it must be combined with selected chemical additives and modifiers to achieve the various properties desired in vinyl end products. Once these are added, the resulting material -- vinyl compound -- can be converted into an almost limitless range of applications. It is the only plastic that can be made thin and flexible enough for wall coverings, yet rigid and tough enough for siding on buildings. Depending on the additives and modifiers used, vinyl compound can be used indoors or outside, be crystal clear or opaque, and matched to virtually any color in the rainbow.

Plastics:

There are two main groups of plastics:

1. THERMOPLASTICS soften with heat and harden with cooling. Some typical thermoplastics are: Acrylic (Perspex) Acrylo-nitrile (Nylon) Polyethylene (Polythene) white solid substance, the Polymer of Ethylene Polypropylene Poly Vinyl Acetate (PVA) Poly Vinyl Chloride (PVC) Polystyrene and ABS PTFE (Teflon)

2. THERMOSETS are cured or hardened by heat. Some typical thermosets are: Bakelite Epoxy Melamine Polyester Polyurethane

Basic Terms of Maintenance, Operations and System Components

Viscosity : resistance of a fluid to flow. This resistance acts against the motion of any solid object through the fluid and also against motion of the fluid itself past stationary obstacles. Viscosity also acts internally on the fluid between slower and faster moving adjacent layers.
Additive : A chemical substance added to a petroleum product to impart or improve certain properties.
Amorphous : shapeless.or of no particular type. No organization; formless, or lacking distinct crystalline structure. Compound a substance composed of atoms of two or more elements in chemical combination
Demulsibility : The ability of oil to separate from water.
Dichloride : A chemical compound containing two chlorine atoms bound to another element or radical.
Electrolysis : passage of an electric current through a conducting solution or molten salt that is decomposed in the process
Ethylene Composition : C2H4 (CH2=CH2) Properties: A colorless, flammable gas with a slightly sweet odor, soluble in water. Made from hydrocarbon feedstocks, such as natural gas liquids or crude oil. Produced almost exclusively from the pyrolysis of hydrocarbons in tubular reactor coils installed in externally fired heaters.
Monomer :A molecule that can combine with others to form a polymer.
Oxidation : The chemical combination of a substance with oxygen.
Polymer : chemical compound with high molecular weight consisting of a number of structural units linked together by covalent bonds
Polymerization : The bonding of two or more monomers to form a polymer
Resin : any of a class of amorphous solids or semisolids. Resins are found in nature and are chiefly of vegetable origin. They are typically light yellow to dark brown in color; tasteless; odorless or faintly aromatic; translucent or transparent; brittle, fracturing like glass; and flammable, burning with a smoky flame. Resins are soluble in alcohol, ether, and many hydrocarbons but are insoluble in water. When heated, they soften and finally melt. Their chemical composition varies, but most are mixtures of organic acids and esters.
Vinyl chloride : A flammable gas, CH2:CHCl, used as a monomer for polyvinyl chloride.

Task/ Quiz

Go to the basic math link and study pages 11 thru 19. Lesson 3 quiz will contain questions on this material.

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