Нефтепереработка

III. Нефтепереработка

1. Electric desalting unit

Vocabulary to be remembered:

crude oil \ crude - сырая нефть, нефть-сырец

refinery - нефтеперерабатывающий завод

vessel - труба

finished product - товарная продукция

capacity - производительность

manufacturing cost - издержки производства

ash content - содержание золы

residual product - осадочный продукт

dehydrating - обезвоживание

desalting - обессоливание

operating practice - существующая практика

expediency - рентабельность

tank -емкость

settling tank - отстойник

High contents of salt and water in the crude oil are known to cause great losses to refineries handling such crudes. Salts give deposits in still and heat exchanger tubes, where high salt content crudes are processed, thus considerably affecting the heat transfer rate and causing corrosion of vessels, machinery, valves and pipes as well as increased fuel consumption, loss in capacity of the processing units, and great increase of finished products manufacturing costs. Apart from this, increased ash content in residual products makes their full utilization a difficult and sometimes even impossible thing.

Considering all said above, particular attention has been paid by the petroleum industry during the last years to problems involves in purification of crudes before their refining. Electric dehydrating and desalting processes became widespread as a result.

Operating practice as well as repeated engineering and economic calculations have confirmed the expediency of thorough preparation of crudes in refineries.

The electric desalting unit described below is a most frequent type having recently found a wide application. The unit comprises two spherical electric dehydrating tanks of 600 cu.m volume each and a set of settling tanks. It can operate either in two or three stages, depending on the quality of the crude to be handled.

EXERCISES

2. Flow diagram of electric desalting unit

Vocabulary to be remembered:

Flow diagram - технологическая схема

storage tank - резервуар для хранения

strainer - фильтр

vessel - резервуар, емкость

heat exchanger group - блок теплообменников

steam heater - паровой подогреватель

settling tank - отстойник

sediment - осадок

caustic - каустическая сода, каустик

distribution head - распределительная головка

electric dehydrating tank - электродегидратор

fresh water - пресная вода

precipitation space - зона отстоя

drainage system - система стоков, канализация

cooler холодильник

water requirement - расход воды

The flow diagram of an electric desalting unit acting in three stages bases on the following. Crude oil flows along pipes from storage tanks to the suction side of a crude pump which delivers it through strainers into a heat exchanger group. In the latter the crude is heated to 60^o or 70^oC by utilizing the heat contained in the desalted crude. From the heat exchangers the crude continues its flow into steam heaters where its temperature is raised to 110^o or 115^oC on account of steam.

Provisions are made for injecting water into the crude stream after the heaters, if necessary. Not only water but also demulsifying agent can be introduced in the above points.

The crude oil, water and demulsifier mixture leaving the heaters are directed into horizontal settling tanks where part of the water with salts dissolved in it and most of the sediments fall out. The crude, having partly rejected its water and sediment in the settlers, flows then into a line where a caustic solution and, if necessary, hot water and demulsifier are added to it. The caustic is delivered in the required proportion by a controlled-volume feed pump.

Now the crude mixed with water, caustic and demulsifying agent enters the spherical dehydrating tank through three distribution heads opening into clearances between electrode pairs. Passing between them the crude stream is subjected to the effect of a high-potential electrostatic field after which it enters a precipitation space.

The water with the salts dissolved in it settles at the tank bottom, whereafter it is released into the drainage system.

A pressure within 5 and6 kg. per sq. cm and a temperature about 112 C are maintained in the electric dehydrating tank. A pipe transfers the partly desalted and dehydrated crude accumulating in the top portion of the sphere into the second electric dehydrating tank. Fresh hot water and, if necessary, caustic solution and demulsifier are injected into the transfer pipe. The finally dehydrated and desalted crude leaving the secondary dehydrating tank passes through heat exchangers and coolers into a purified crude storage tank.

The capacity of the desalting unit of the described type is 2 million tons per year and is highly effective. If the crude to be treated contains, for instance, about 2000 mg of salt per litre and about 3% of water, the desalting process will reduce the salt content to 10 or 20 mg. per litre and the water content to 0.2% or less, down to traces.

The water requirements for the crude washing reach 10% of the crude quantity handled. About 10g of 92% caustic solution are required per ton of crude oil. Superior grade demulsifying agents are then necessary in quantities as small as several grammes per ton of the crude handled.

EXERCISES

Ex.1. Translate into English:

1. Сырая нефть течет... 2. Она нагревается ... 3. Температура повышается до ... 4. Деэмульгатор вводится ... 5. Раствор каустической соды вводится в заданном количестве... 6. Смесь поступает в электродегидратор. 7. Она подвергается воздействию ... 8.Вода осаждается на дно. 9. Прием сырьевого насоса... 10. Температура повышается за счет пара. 11. Каустическая сода подается дозировочным насосом.. 12. Распределительные головки. 13. Резервуары для хранения обессоленной нефти.

Ex. 2. Answer the questions: