Introduction of Unit 1 Crude Distillation Unit

3. 3 Crude Feed Crude oil feed is held in storage tanks, 001 to 006, 008 and 010 and is pumped to the crude unit by any combination of four Crude Charge Pumps, 5008-01, 5008-02, 5008-04 and 5008-89. Pumps 5008-02, 5008-04 and 5008-89 are variable speed pumps. Pump 5008-48 (Spike Pump) takes suction from the 14” header from tanks 001-008/010, and discharges into the suction lines to the main crude charge pumps. This pump is used to bring a new tank onto feed the unit, the initial feed on 5008-48 would be 20 to 30 m3/hr, increasing to 100-120 m3/hr max as conditions allow. This pump is used to limit the amount of water in crude feed when a new tank is charged to the unit, or to control the amount feed to the unit from a slop tank containing high RVP product. Pump 5008-03 is used for transfers on Offsites. Normally three feed pumps are on at any one time with the fourth being used as a spare. Crude feed rates are determined by the quantity and quality of end product required, the flow being controlled by three flow control valves, 01FCV 026, 01FCV 027, 01FCV 864 and 01FIC 4900 operated from the Main Control Room (MCR). For each pump there are facilities for stopping and starting the motors via hand switches HS 132, HS 133, HS 826N and HS 4931 in the MCR. Indication of motor performance is shown by ammeters on the control panel. Each pump is capable of two thirds design capacity of the crude unit. When charging through two or more FCV’s, one FCV is operated in manual control to maintain battery limits pressure between 16 kg/cm2-26 kg/cm2, monitored by 50 PI 337. The crude is preheated by exchange with hot products and pump-arounds. Crude feed enters the unit via a 10” line from the west battery limits; at this point a line branches off with a block valve to provide a facility to flush the crude residue rundown line. The 10” crude feed expands to a 12” line after the injection of desalting water and demulsifier. Approximately 25% of water used for desalting is injected by Desalter Water Pumps 0108-36 and 0108-37 via flow meters 01 FT 011 & 01 FT 3522 and hand control valves before entering the heat exchangers. Demulsifying chemical used for breaking emulsions in the Desalter is also injected. This chemical is pumped from the Demulsifier Storage Tank 0106-49, via metering pump 0108-83. Note: During unit start-up and shutdown, a 17. 5kg/cm2 steam supply is provided downstream of the battery limits block valve for steam purging of the crude preheat system. The crude feed divides into two streams and passes through the tube side of Crude – Reduced Crude Product Exchangers 0107-81A/B and Crude – Crude Overhead Product Exchangers 0107-81C/D operating two in parallel and two in series gaining heat from the shell side products. The amount of heat gained will vary with the reduced crude flow rate and the requirements of upstream heat exchangers which also remove heat from the reduced crude. On leaving the exchangers, the crude feed connects to become one stream and enters the tube side of the Crude – Crude Tower Overhead Exchangers, 0107-82A~D with the four exchangers operating two in parallel and two in series. Heat is gained from the shell side of these exchangers and the two crude streams join up in a common feed line on the outlet side. To prevent excessive condensation of the Crude distillation tower overheads in exchangers, 0107-82A~D, the crude feed can be partially by passed around the heat exchangers by opening a 6” by pass block valve and pinching in the 12” inlet line block valves. The bypass provides control of the overhead product temperature to give sufficient lift for the vapour/liquid mixture to enter the Crude Tower Overhead Condenser 0107-01A~G. Crude feed flows to the tube side of the Crude – Kerosene Pump-around Low Level Exchanger, 0107-83, where it gains heat from the shell side stream. The crude then splits into two streams feeding the tube side of the Crude – Kerosene Pump-around High Level Exchanger 0107-84 and the Crude – LGO Product Exchanger 0107-121 arranged in parallel where it gains heat from the shell side product streams respectively. The two streams join together and flows through the Desalter pressure control valve, 01 PCV 015N (controlled from the MCR) which adjusts the flow of crude to the base of the Desalter according to the outlet pressure. The Desalter 0106-95 removes solids and water containing dissolved salts from the crude and operates at approximately 129°C and 9. 8 kg/cm2g The crude feed may be by-passed around the Desalter by opening the by-pass valve downstream of 01 PCV 015N, and closing the Desalter outlet block valve on the suction line to the Crude Furnace Charge Pumps, 0108-126/127. This method is used on initial start-up to fill the crude Preheat Train, before filling the Desalter more slowly at a later stage.