If you can translate these word-combinations your total score is 72. Congratulations! 5 page

When chilled to very cold temperatures, approximately - 260 degrees Fahrenheit, natural gas changes into a liquid and can be stored in this form. Because it takes up only 1/600th of the space that it would in its gaseous state, Liquefied natural gas (LNG) can be loaded onto tankers (large ships with several domed tanks) and moved across the ocean to deliver gas to other countries. When this LNG is received, it can be shipped by truck to be held in large chilled tanks close to users or turned back into gas to add to pipelines.

When the gas gets to the communities where it will be used (usually through large pipelines), the gas is measured as it flows into smaller pipelines called “mains”. Very small lines, called “services”, connect to the mains and go directly to homes or buildings where it will be used.

How is Natural Gas Measured

We measure and sell natural gas in cubic feet (volume) or in British Thermal Units (heat content). Heat from all energy sources can be measured and converted back and forth between British thermal units (Btu) and metric units.

One Btu is the heat required to raise the temperature of one pound of water one degree Fahrenheit. Ten burning kitchen matches release 10 Btu. A candy bar has about 1000 Btu. One cubic foot of natural gas has about 1031 Btu. A box 10 feet deep, 10 feet long, and 10 feet wide would hold one thousand cubic feet of natural gas.

Description of a Natural Gas Processing Plant

There are a great many ways in which you can configure the various unit processes used in the processing of raw natural gas. The block flow diagram is a generalized, typical configuration for the processing of raw natural gas from non- associated gas wells. It shows how raw natural gas is processed into sales gas pipelined to the end user markets. It also shows how processing of the raw natural gas yields these by-products:

• Natural gas condensate

• Sulfur

• Ethane

• Natural gas liquids (NGL): propane, butanes and C₅+ (which is the commonly used term for pentanes plus higher molecular weight hydrocarbons)

Raw natural gas is commonly collected from a group of adjacent wells and is first processed at that collection point for removal of free liquid water and natural gas condensate. The condensate is usually then transported to an oil refinery and the water is disposed of as wastewater.

The raw gas is then pipelined to a gas processing plant where the initial purification is usually the removal of acid ga- ses (hydrogen sulfide and carbon dioxide). There are many processes that are available for that purpose as will be shown in the flow diagram, but amine treating is the most widely used process. In the last ten years, a new process based on the use of polymeric membranes to dehydrate and separate the carbon dioxide and hydrogen sulfide from the natural gas stream is gaining acceptance.

The acid gases removed by amine treating are then routed into a sulfur recovery unit which converts the hydrogen sul-

fide in the acid gas into elemental sulfur. There are a number of processes available for that conversion, but the Claus process is by far the one usually selected. The residual gas from the Claus process is commonly called tail gas and that gas is then processed in a tail gas treating unit (TGTU) to recover and recycle residual sulfur-containing compounds back into the Claus unit. There are a number of processes available for treating the Claus unit tail gas. The final residual gas from the TGTU is incinerated. Thus, the carbon dioxide in the raw natural gas ends up in the incinerator flue gas stack.

The next step in the gas processing plant is to remove water vapor from the gas using either the regenerable absorp- tion in liquid triethylene glycol (TEG), commonly referred to as glycol dehydration, or a Pressure Swing Adsorption (PSA) unit which is regenerable adsorption using a solid adsorbent. Other newer processes requiring a higher pressure drop like membranes or dehydration at supersonic velocity using, for example, the Twister Supersonic Separator may also be consi- dered.

Mercury is then removed by using adsorption processes (as shown in the flow diagram) such as activated carbon or rege- nerable molecular sieves.

Nitrogen is next removed and rejected using one of the three processes:

• Cryogenic process using low temperature distillation. This process can be modified to also recover helium, if desired.

• Absorption process using lean oil or a special solvent as the absorbent.

• Adsorption process using activated carbon or molecular sieves as the adsorbent. This process may have limited applica- bility because it is said to incur the loss of butanes and heavier hydrocarbons.

The next step is to recover of the natural gas liquids (NGL) for which most large, modern gas processing plants use ano- ther cryogenic low temperature distillation process involving expansion of the gas through a turbo-expander followed by

distillation in a demethanizing fractionating column. 1 Some gas processing plants use lean oil absorption process rather than the cryogenic turbo-expander process.

The residue gas from the NGL recovery section is the final, purified sales gas which is pipelined to the end-user markets.

Measures and Definitions

Characteristics of underground storage facilities need to be defined and measured. A number of volumetric measures have been put in place for that purpose:

• Total gas storage capacity: It is the maximum volume of natural gas that can be stored at the storage facility. It is determined by several physical factors such as the reservoir volume, and also on the operating procedures and engineering methods used.

• Total gas in storage: It is the total volume of gas in storage at the facility at a particular time.

• Base gas (also referred to as cushion gas): It is the volume of gas that is intended as permanent inventory in a storage reservoir to maintain adequate pressure and deliverability rates throughout the withdrawal season.

• Working gas capacity: It is the total gas storage capacity minus the base gas.

• Working gas: It is the total gas in storage minus the base gas. Working gas is the volume of gas available to the market place at a particular time.

• Physically unrecoverable gas: The amount of gas that becomes permanently embedded in the formation of the storage facility and that can never be extracted back.

• Cycling rate: It is the average number of times a reser- voir’s working gas volume can be turned over during a specific period of time. Typically the period of time used is one year.

• Deliverability: It is a measure of the amount of gas that can be delivered (withdrawn) from a storage facility on a daily basis. It is also referred to as the deliverability rate, with-drawal rate, or withdrawal capacity and is usually expressed in terms of millions of cubic feet of gas per day (MMcf/day) that can be delivered.

• Injection capacity (or rate): It is the amount of gas that can be injected into a storage facility on a daily basis. It can be thought of as the complement of the deliverability. Injection rate is also typically measured in millions of cubic feet of gas that can be delivered per day (MMcf/day).

The measurements above are not fixed for a given storage facility. For example, deliverability depends on several factors including the amount of gas in the reservoir and the pressure etc. Generally, a storage facility’s deliverability rate varies directly with the total amount of gas in the reservoir. It is at its highest when the reservoir is full and declines as gas is withdrawn. The injection capacity of a storage facility is also variable and depends on factors similar to those that affect deliverability. The injection rate varies inversely with the total amount of gas in storage. It is at its highest when the reservoir is nearly empty and declines as more gas is injected. The stora- ge facility operator may also change operational parameters. This would allow, for example, the storage capacity maximum to be increased, the withdrawal of base gas during very high demand or reclassifying base gas to working gas if technologi- cal advances or engineering procedures allow.

Depleted Gas Reservoir

In order to maintain working pressures in depleted re- servoirs, about 50 percent of the natural gas in the formation must be kept as cushion gas. However, since depleted reservoirs were previously been filled with natural gas and hydro- carbons, they do not require the injection of gas that will become physically unrecoverable as this is already present in the formation. This provides a further economic boost for this type of facility, particularly when the cost of gas is high. Ty- pically, these facilities are operated on a single annual cycle; gas is injected during the off-peak summer months and withdrawn during the winter months of peak demand.

A number of factors determine whether or not a depleted gas field will make an economically viable storage facility. Geographically, depleted reservoirs should be relatively close to gas markets and to transportation infrastructure (pipelines and distribution systems) which will connect them to that market. Since the fields were at one time productive and con- nected to infrastructure distance from market is the dominant geographical factor. Geologically, it is preferred that depleted reservoir formations have high porosity and permeability. The porosity of the formation is one of the factors that determines the amount of natural gas the reservoir is able to hold. Permeability is a measure of the rate at which natural gas flows through the formation and ultimately determines the rate of injection and withdrawal of gas from storage.

Aquifer Reservoir

If the aquifer is suitable, all of the associated infra-struc- ture must be developed from scratch, increasing the develop- ment costs compared to depleted reservoirs. This includes installation of wells, extraction equipment, pipelines, dehydra- tion facilities, and possibly compression equipment. Since the aquifer initially contains water there is little or no naturally occurring gas in the formation and of the gas injected some will be physically unrecoverable. As a result, aquifer storage typically requires significantly more cushion gas than deple- ted reservoirs; up to 80% of the total gas volume. Most aqui- fer storage facilities were developed when the price of natural gas was low, meaning this cushion gas was inexpensive to sac- rifice. With rising gas prices aquifer storage becomes more ex- pensive to develop.

A consequence of the above factors is that developing an aquifer storage facility is usually time consuming and expen- sive. Aquifers are generally the least desirable and most expen- sive type of natural gas storage facility.

Salt Formation

Salt caverns are usually much smaller than depleted gas reservoir and aquifer storage facilities. A salt cavern facility may

occupy only one one-hundredth of the area taken up by a depleted gas reservoir facility. Consequently, salt caverns cannot hold the large volumes of gas necessary to meet base load storage requirements. Deliverability from salt caverns is, however, much higher than for either aquifers or depleted re- servoirs. This allows the gas stored in a salt cavern to be with- drawn and replenished more readily and quickly. This quick cycle-time is useful in emergency situations or during short periods of unexpected demand surges.

Although construction is more costly than depleted field conversions when measured on the basis of dollars per thou- sand cubic feet of working gas, the ability to perform several withdrawal and injection cycles each year reduces the effective cost.

Future of Storage Technology

Research is being conducted on many fronts in the gas storage field to help identify new improved and more economical ways to store gas. Research being conducted by the US Energy department is showing that salt formations can be chilled allowing for more gas to be stored. This will reduce the size of the formation needed to be treated, and have salt extrac- ted from it. This will lead to cheaper development costs for salt formation storage facility type. Another aspect being looked at, are other formations that may hold gas. These include hard rock formations such as granite, in areas where such for- mations exists and other types currently used for gas storage do not. In Sweden a new type of storage facility has been built, called “lined rock cavern”. This storage facility consists of installing a steel tank in a cavern in the rock of a hill and sur- rounding it with concrete. Although the development cost of such facility is quite expensive, its ability to cycle gas multiple times compensates for it, similar to salt formation facilities. Finally, another research projected sponsored by the Depart- ment of Energy, is that of hydrates. Hydrates are compounds formed when natural gas is frozen in the presence of water.

The advantage being that as much as 181 standard cubic feet of natural gas could be stored in a single cubic foot of hydrate.

Safety

Terrorism or deliberate provocation of effusion and inflammation of gas is at this moment the most likely scenario of possible big disaster. Because of this problem America has strictly set the rules that are determining sail with tankers full of LNG. Fast ships are following tanker and protecting it when it sails to terminal and upon cargo unloading. When in sail, tanker cannot be approached by another ship on the distance of 450 meters from each side and 3.2 kilometers in front and behind the ship. For the offenders higher convictions are determined (up to ten years of imprisonment), but that will probably not discourage suicidal terrorists to attempt to crash into a tanker. Legal regulation of the safety is a difficult thing because not even America has completely regulated laws at this moment (for instance, it isn’t completely defined what the coast guard should do if some marine vehicle sails into a safety zone around tankers), and more worrying is the fact that terrorists managed to crash themselves with the craft to a well guarded military ship USS Cole.

The Greenhouse Effect

Pattern of absorption bands created by greenhouse gases in the atmosphere and their effect on both solar radiation and upgoing thermal radiation

When sunlight reaches the surface of the Earth, some of it is absorbed and warms the surface. Because the Earth’s sur- face is much cooler than the sun, it radiates energy at much lon- ger wavelengths than the sun does, peaking in the infrared at about 10 jam. The atmosphere absorbs these longer wave- lengths more effectively than it does the shorter wavelengths from the sun; The absorption of this longwave radiant energy warms the atmosphere; the atmosphere is also warmed by transfer of sensible and latent heat from the surface. Green- house gases also emit longwave radiation both upward to

space and downward to the surface. The downward part of this longwave radiation emitted by the atmosphere is the “green- house effect”. The term is a misnomer though, as this process is not the mechanism that warms greenhouses.

On earth, the most abundant greenhouse gases are, in order of relative abundance:

• water vapor

• carbon dioxide

• methane

• nitrous oxide

• ozone

• CFCs

The most important greenhouse gases are:

• water vapor, which causes about 36-70% of the green- house effect on Earth. (Note clouds typically affect climate differently from other forms of atmospheric water.)

• carbon dioxide, which causes 9-26%

• methane, which causes 4-9%

• ozone, which causes 3-7%

Note that this is a combination of the strength of the green- house effect of the gas and its abundance. For example, methane is a much stronger greenhouse gas than C0₂—about 25 times more heat absorptive, but is present in much smaller concentra- tions.

It is not possible to state that a certain gas causes a certain percentage of the greenhouse effect, because the influences of the various gases are not additive. (The higher ends of the ranges quoted are for the gas alone; the lower ends, for the gas counting overlaps.) Other greenhouse gases include, but are not limited to, nitrous oxide, sulfur hexafluoride, hydroflu- orocarbons, perfluorocarbons and chlorofluorocarbons. A potentially significant greenhouse gas not yet addressed by the IPCC (or the Kyoto Protocol) is nitrogen trifluoride.

The major atmospheric constituents (nitrogen, N₂ and oxy- gen, 0₂) are not greenhouse gases. Nor is the approximately 1% of argon, Ar. This is because homonuclear diatomic molecules such as N₂ and

0₂ and monatomic molecules such as Ar neither absorb nor emit infrared radiation, as there is no net change in the dipole moment of these molecules when they vibrate. Molecular vibrations occur at energies that are of the same magnitude as the energy of the photons on infrared light. Heteronuclear diatomics such as CO or HC1 absorb IR; how- ever, these molecules are short-lived in the atmosphere owing to their reactivity and solubility. As a consequence they do not contribute significantly to the greenhouse effect.

Late 19th century scientists experimentally discovered that N₂ and 0₂ did not absorb infrared radiation (called, at that time, «dark radiation») and that C0₂ and many other gases did absorb such radiation. It was recognized in the early 20th century that the known major greenhouse gases in the atmo- sphere caused the earth’s temperature to be higher than it would have been without the greenhouse gases.

Part II

PIPELINES

UNIT III

A pipeline comprises all parts of the physical facility through which liquids(crude oil,petroleum products) or gases (natural gas, carbon dioxide) are transported including pipe, valves and other equipment at­tached to the pipe, compressor units, pump stations, metering stations, regulator stations, de­livery stations, holders and fab­ricated assemblies.

Pipelines are the safest and most efficient means of trans­porting crude oil and natural gas from producing fields to refineries and processing plants and of distributing petroleum products and natural gas to the consumer.

The first gas pipeline was installed in Genoa, Italy in 1802 to carry gas for street lighting.

Section 1. Basic course

Task 1. Piping. Pipeline Transport

Within industry, piping is a system of pipes used to convey fluids and gases, from one location to another. The engineering discipline of piping design studies the best and most efficient manner of transporting fluid to where it is needed.

Date: 2015-12-24; view: 638