 |
|
Text 3. Natural Gas Processing
Natural gas is a gaseous fossil fuel consisting primarily of methane but including significant quantities of ethane, propane, butane, and pentane.
Natural gas is often informally referred to as simply gas, especially when compared to other energy sources. Before natural gas can be used as a fuel it must undergo extensive processing to remove almost all materials other than methane. The by-products of that processing include ethane, propane, butanes, pentanes and higher molecular weight hydrocarbons, elemental sulfur, and sometimes helium and nitrogen. Processed natural gas is originally harmless for the human being, however, natural gas is a simple asphyxiant and can kill if it displaces air to the point where the oxygen content will not support life.
Natural gas can also be hazardous to life due to its explosive property. Natural gas is lighter than air and so tends to escape into the atmosphere. But when natural gas is confined, such as within a house, gas concentrations can reach explosive mixtures and, if ignited, results in blasts that could destroy buildings. Methane has a lower explosive limit of 5 % in air, and an upper explosive limit of 15 %. Explosive concerns with compressed natural gas used in vehicles are almost non-existent due to escaping nature of the gas and the need to maintain concentrations between 5 % and 15 %.
Natural gas processing plants are used to purify the raw natural gas extracted from underground gas fields and brought up to the surface by gas wells. The processed natural gas, used as a fuel by residential, commercial and industrial consumers, is almost pure methane and is very much different from the raw natural gas. Raw natural gas typically consists primarily of methane (CH4), the shortest and lightest hydrocarbon molecule. It also contains varying amounts of heavier gaseous hydrocarbons (ethane (C2H6), propane (C3H8), normal butane (n-C4H10), isobutane (i-C4H10), pentanes and even higher molecular weight hydrocarbons. When processed and purified into finished by-products, all of which are collectively referred to NGL (Natural Gas Liquids). Raw natural gas also contains acid gases (carbon dioxide (CO2), hydrogen sulphide (H2S) and other gases (nitrogen (N2) and helium (He); water vapour and liquid water; perhaps some natural gas condensate and / or crude oil; very small amounts of mercury in elementary form.
The raw natural gas must be purified to meet the quality standards specified by the major pipeline transmission and distribution companies. Those quality standards vary from pipeline to pipeline and are usually a function of a pipeline system design and the markets.
Raw natural gas comes primarily from any one of three types of wells: crude oil wells, gas wells and condensate wells.
Natural gas that comes from crude oil wells is typically termed associated gas. This gas can exist separately from the crude oil in the underground formation or dissolve in the crude oil.
Natural gas from gas wells and from condensate wells in which there is little or no crude oil is termed non-associated gas. Gas wells typically produce only raw natural gas, while condensate wells produce raw natural gas with a very low density liquid hydrocarbon called natural gas condensate (sometimes also called natural gasoline or simply condensate).
Raw natural gas can also come from methane deposits in the pores of coal seams. Such gas is referred to as coalbed gas. It is also called sweet gas because it is relatively free of hydrogen sulphide.
The processing of the raw natural gas yields the following products: natural gas condensate, sulfur and ethane.
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 transported to an oil refinery and the disposed water is referred to as wastewater.
The raw gas is then pipelined to a gas processing plant where the initial purification is usually the removal of acid gases (hydrogen sulphide and carbon dioxide). There are many processes that are available for that purpose. In the last ten years a new process based on the use of polymeric membranes to dehydrate and separate the carbon dioxide and hydrogen sulphide from the natural gas stream is gaining acceptance.
The acid gases are then routed into a sulfur recovery unit which converts the hydrogen sulphide in the acid gas into elemental sulfur. The residual gas called tail gas is then processed in a tail gas treating unit (TGTU). The final residual gas from the TGTU is incinerated. Thus, the carbon dioxide in the raw natural gas ends up in the incinerator.
The next step in the gas processing plant is to remove water vapour from the gas using the regenerable adsorption. The newer processes require a higher pressure drop like membranes or dehydration at supersonic velocity.
Mercury is then removed by using absorption processes such as activated carbon or regenerable molecular sieves. Nitrogen is removed and rejected using one of the following processes, such as: cryogenic and absorption. Cryogenic process uses low temperature distillation. This process can be modified to recover helium, if desired.
Absorption process uses lean oil or a special solvent as the absorbent. This process may have limited applicability because of the loss of butanes and heavier hydrocarbons.
The next step is to recover the natural gas liquids (NGL). Most large, modern gas processing plants use cryogenic low temperature distillation process involving expansion of the gas through a turbo-expander. 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.
Exercise 31. Translate the following universal words without a dictionary.
Gas, methane, ethane, propane, butane, pentane, condensate, nitrogen, molecular, atmosphere, limit, commercial, industrial, butane, hydrocarbon, standard, deposit, membrane, polymeric, absorption, cryogenic, absorbent.
Exercise 32. These words are used both as verbs and as nouns. Translate and remember them.
To escape – escape, to pipeline – pipeline, to result – result, to vapour – vapour, to route – route, to process – process, to design – design, to seam – seam, to well – well, to deposit – deposit, to yield – yield, to use – use, to tail – tail.
Exercise 33. Determine the parts of speech of the following words and translate them. Define the affixes, if any.
Informally, natural, well, extensive, purify, purification, harmless, hazardous, concentration, explosive, non-existent, residential, consumer, incinerator, incinerated, regenerable, applicability, transmission, distribution, usually, primarily, dissolved, associated, non-associated, pipelined, initial, recovery, residual, supersonic, dehydration, modify, heater.
Exercise 34. Translate the word combinations with the word ‘gas’.
Natural gas, simple gas, processed gas, hazardous gas, explosive gas, associated gas, non-associated gas, coalbed gas, sweet gas, acid gas, tail gas, residual gas, incinerated gas, purified gas, pipelined gas.
Exercise 35. Translate “noun + noun” word combinations.
Energy source, gas field, gas deposit, transmission company, distribution company, quality standard, pipeline design, oil well, gas well, condensate well, coal seam, methane deposit, pressure drop, temperature distillation, absorption process, oil absorption, end user, gas stream, sulfur recovery unit.
Exercise 36. Match the English terms in the left column with their Ukrainian equivalents in the right column.
| 1. by-product 2. field 3. vapour 4. material 5. mercury 6. pipeline 7. absorption 8. oil refinery 9. pore 10. incinerator | a) речовина b) перекачувати по трубах c) ртуть d) родовище e) поглинання f) нафтопереробний завод g) спалювальна піч h) свердловина i) побічний продукт j) пара |
Exercise 37. Match the synonyms.
| a) pore b) crude c) safe d) refine e) dangerous f) explosion g) deposit h) transmit i) process j) user |
Exercise 38. Translate the following word combinations. Comment upon the grammar forms.
Is referred to as simply gas; can be used as a fuel; must undergo; can be hazardous; consists of methane; tend to escape into the atmosphere; is lighter than air; results in blasts; to purify the gas; could destroy buildings; must be purified; to meet the quality standards; vary from pipeline to pipeline; is termed non-associated gas; can come from me-thane deposit; is called sweet gas; yields the by-products; is commonly collected; is processed at the collection point; is gaining acceptance; are routed into recovery unit; is processed in a treating unit; to remove vapour; is removed by cryogenic process; may have limited applicability; is pipelined to the end-user markets.
Exercise 39. Define whether the statements are true or false. Correct if the statement is false.
1. Before natural gas can be used as a fuel it must undergo extensive processing to remove all materials. 2. Natural gas is lighter than air and so tends to escape into the atmosphere. 3. Natural gas processing plants are used to calculate the volume of raw natural gas. 4. Natural gas that comes from crude oil wells is typically termed non-associated gas. 5. Natural gas condensate is relatively free of hydrogen sulphide. 6. Natural gas from gas wells is referred to as coalbed gas. 7. The processing of the raw natural gas yields the following by-products: natural gas condensate, sulfur and ethane.
Exercise 40. Match the definitions in the left column with the terms in the right column.
| 1. The natural gas which contains almost pure methane | a) associated gas |
| 2. The natural gas that comes from crude oil wells | b) coalbed gas |
| 3. The natural gas from gas wells and condensate wells | c) processed natural gas |
| 4. The raw natural gas with a very low density liquid hydrocarbon | d) tail gas |
| 5. The raw natural gas that comes from methane deposits in the pores of coal seams | e) non-associated gas |
| 6. The residual gas resulted from the process of the acid gases conversion | f) natural gas condensate |
Exercise 41. Complete the sentences using English equivalents of the words in brackets in the appropriate form.
1. Before (природний газ) can be used as a fuel it must undergo extensive (обробка). 2. (Газопереробний завод) are used to purify (неочищений природній газ) extracted from underground gas (родовище) and brought up to the surface by gas (свердловина). 3. (Супутній газ) can exist separately from the crude oil in the underground formation or dissolve in the crude oil. 4. Condensate wells produce raw natural gas with a very low density liquid (вуглеводень) called natural gas condensate. 5. (Газ, виділений з вугільних пластів) is relatively free of (сульфат водню). 6. The condensate is usually transported to an (нафтопереробний завод). 7. The raw gas is then pipelined to a gas processing plant where (початкове очищення) is usually the removal of (кислотний газ). 8. The residual gas is processed in a (секція переробки залишкового газу). 9. The acid gases are routed into a (секція регенерації сірки). 10. The (двоокис вуглецю) in the raw natural gas ends up in the (спалювальна піч). 11. Absorption process uses (збідніла нафта) or a special (розчинник).
Exercise 42. Translate the following sentences.
1. Природний газ – це газоподібне викопне паливо. 2. Природний газ в основному складається з метану, але й включає як значну кількість етану, пропану, бутану і пентану, так і двоокис вуглецю, азоту, гелію, сульфату водню. 3. Перш ніж газ можна буде використовувати як паливо, він зазнає інтенсивної переробки. 4. Природний газ – це задушлива отруйна речовина, що витісняє вміст кисню у повітрі. 5. Природний газ може бути небезпечним через свої вибухові властивості. 6. Газопереробні заводи використовуються для очищення сировинного природного газу, який видобувається з підземних газових родовищ і піднімається з підземних газових свердловин. 7. Очищений природний газ, який використовується мешканцями будинків, комерційними і промисловими споживачами, є майже чистим метаном. 8. Очищення сировинного природного газу повинно відповідати стандартам якості, визначеним більшістю транспортних і розподільчих компаній. 9. Супутній газ із нафтових свердловин може існувати окремо від сировинної нафти у підземних нашаруваннях або розчинятися у сировинній нафті. 10. Природний газовий конденсат, який має низьку концентрацію вуглеводню, називають також природним бензином або просто конденсатом. 11. Вугільний газ видобувають з метанових родовищ у свердловинах вугільних пластів. 12. Природний газ спочатку збирається з прилеглих свердловин і обробляється, щоб виділити вільну воду і природний газовий конденсат. 13. Сировинний газ передається на газопереробний завод для видалення кислотного газу. 14. Процес регенерації перетворює сульфат водню у кислотному газі у просту сірку. 15. Газ, що залишився після переробки, спалюється. 16. Ртуть видаляється у процесі абсорбції. 17. Очищений газ, який призначається для продажу, постачається на споживчий ринок.
Exercise 43. Answer the questions.
1. What is natural gas? 2. What materials does natural gas consist of? 3. Why must natural gas undergo extensive processing? 4. Why is natural gas hazardous for our life? 5. What plants are used to purify the raw natural gas? 6. How is the processed natural gas used? 7. What types of wells does raw natural gas come from? 8. What natural gas is termed associated gas? 9. What natural gas is called non-associated gas? 10. What is natural gas condensate? 11. How is raw natural gas from methane deposits of coal seams called? 12. Where is raw natural gas first processed? 13. What is the initial purification at a gas processing plant? 14. What process results in elemental sulfur production? 15. What is used to remove water vapour from the gas? 16. How is mercury removed? 17. What processes are used to remove and reject nitrogen? 18. What processes are used to recover natural gas liquids? 19. What gas is considered to be pipelined to the end-user markets?
Exercise 44. Memorize the following words and word combinations to text 4.
Efficient – ефективний
elaborate – детальний, дуже складний
in many instances – у багатьох випадках
particular – окремий
facilities (pl.) – засоби
essential – головний, необхідний
gathering – збирання
interstate – міждержавний
wellhead – гирло свердловини
processing plant – переробний завод
sour gas – газ із домішками
contents – зміст, склад
install – встановлювати
sweeten – нейтралізувати, видаляти сірку
intrastate – той, що в межах держави
boundary – кордон
lateral – другорядний
steel mill – сталеливарний завод
fold – згинати
weld – зварювати
seemless – безшовний
ship – відвантажувати
coating – покриття
corrode – іржавіти
moisture – волога
rust – іржа; іржавіти
tar – смола
enamel – емаль; покривати емаллю
epoxy – епоксид
ward off – запобігати
punch – пробивати отвори
noticeable – гідний уваги, помітний
deliverability – пропускна потужність
cathodic protection – катодний захист
Exercise 45. Read and translate text 4. Make the plan of its retelling.