Rectification Zone

Vacuum Column have ejectors to maintain the vacuum in the column. Downstream of ejectors condensers are installed to condense the vapour coming out of the ejector. Many people ask why the condensers are installed so high while other condensers in different services are installed at much lower height? The following discussion will answer the question.   First lets see a typical arrangement of a vacuum column overhead circuit with operating pressures in the following diagram.   From the pressure values, it can be seen that the pressure in the hot well chamber is around 0.16 Kg/cm2(g), while the pressure at the Booster Condenser outlet is 70 mm Hg (a). Since the condenser outlet is at a lower pressure than the hot well vessel, the liquid will try to travel up the boot leg of the condenser.   But how far the liquid go up? The liquid will go up, upto a level where it will balance out the pressure difference. Now lets calculate the pressure difference:   Pressure in Hot w

1.   What is the purpose of desalter? Ø Removal of salts dissolved in water. Ø Removal of silts and sediments. Ø Removal of water 2.   What are the harmful effects if desalting is not done? Ø Corrosion of equipments. Ø Plugging / chokage of tubes, tray valves. Ø Chances of over pressurisation due to water. Ø High heat load requirement in furnace due to presence of water. 3.   What are the major steps in desalting? Ø Addition of demulsifier. Ø Increasing temperature Ø Addition of wash water. Ø Mixing of Crude and Water through PDV. Ø Coalescence of water in the electric field. Ø Settling and removal of brine. 4.   One of the purposes of desalting is to remove water from crude. Then why additional water is added to desalter? Water present in the crude is about 0.2 to 0.5 vol%. These small quantities of water are very finely dispersed in the crude. On application of electric field, these water particles takes longer time to coalescenc

Inherently, crude contains some amount of salts which is present with water in a dissolved state. This salt is required to be removed from crude, other wise the salt will form acids on hydrolysis at high temperature inside crude heaters and will cause corrosion in the equipment. For removal of these salts, desalters are provided. However, the desalters are not 100% efficient in removing the salt. Hence some amount of salts is always present at the outlet of the desalters which gets hydrolysed inside crude heaters and form acids. Pure acids is present in vapour phase in the crude overhead circuit and is not corrosive. However when it comes in contact with water vapour and condenses along with the water droplet it is corrosive and detrimental to the equipment. Hence water dew point in the crude overhead circuit is an important parameter to control corrosion. By definition, dew point is the maximum temperature at which 1st drop of liquid will form, in a mixture at a given pressure. No

Date: 09-June-2017 Time: 1050 hrs Sequence of Events: 1. Out of 4 running crude booster Pumps, 3 pumps tripped. Crude flow decreased from 1820 MT/hr to 650 MT/hr. 2. Another crude booster pump was immediately started and crude flow increased from 620 MT/hr to 1200 MT/hr with in 3-4 minutes. 3. Third and fourth crude pump could not be started immediately, hence flow was maintained @ 1200 MT/hr for about one hour. 4. After an hour third crude pump was started and flow was increased upto 1600 MT/hr. 5. Plant was stabilised at 1600 MT/hr by 1400 hrs and the further throughput increased to 1800 MT/hr by 1800 hrs. Action Taken in Panel: 1. Since flash drum level started to decrease, Pass flow to CDU furnace reduced gradually. Flash crude pump discharge was pinched. 2. This resulted in decreasing level of CDU column, hence pass flow to VDU furnace was also reduced gradually. 3. Reduction in pass flows, resulted in higher coil outlet temperatures of the CDU and VDU fur