FACULTY OF ENGINEERING
DEPARTMENT OF CHEMICAL ENGINEERING
NAME: MAITAISHE NATASHA SVOTWA
MODULE:CHEMICAL ENGINEERING TECHNOLOGY: OPERATIONS
TOPIC:DISTILLATION UNITS AND VALVES
LECTURERS:MR HANGONE AND MR THOLE
DUE DATE:14 AUGUST 2018
THIS REPORT IS MY OWN WORK.
SYNOPSISThe distillation process is the cornerstone of many process industries. When a reaction occurs, there are some side reactions; therefore, it is necessary to deploy separation measures such as distillation to achieve a purer desired product.
Since distillation columns are used in many chemical processes, control valve selection is dependent on the process fluid being distilled. However, across many process units, the control valve function in distillation columns is similar. The use of control valves is very critical in the operation of the distillation columns. Control valves are very important in any process where fluid flow must be monitored and manipulated. A basic valve permits or restricts fluid flow at a set time and or adjust the pressure of the system accordingly. A complete control valve consists of the valve itself, an actuator and a valve control device when necessary. An actuator provides the operation force of the valve i.e. it aids with the opening and closing mechanism. The valve control device ensures that the operation conditions are interpreted and manipulated correctly. CITATION Eme14 l 1033 (Emerson Process Management, 2014)In this report, the operation and application of the distillation column and valves will be discussed.
TOC o “1-3” h z u SYNOPSIS PAGEREF _Toc521592822 h ii1.INTRODUCTION PAGEREF _Toc521592823 h 12.OPERATION OF BATCH DISTILLATION UNITS PAGEREF _Toc521592824 h 2FEED VALVE PAGEREF _Toc521592825 h 4REFLUX VALVE PAGEREF _Toc521592826 h 4BOTTOM PRODUCT VALVE PAGEREF _Toc521592827 h 4PRESSURE CONTROL VALVES PAGEREF _Toc521592828 h 4OVERHEAD PRODUCT VALVE PAGEREF _Toc521592829 h 4RE-BOIL VALVE PAGEREF _Toc521592830 h 4TYPES OF TRAYS PAGEREF _Toc521592831 h 53.APPLICATION OF DISTILLATION UNITS PAGEREF _Toc521592832 h 6OIL REFINERY PAGEREF _Toc521592833 h 6DESALINISING WATER PAGEREF _Toc521592834 h 6DISTILLED SPIRITS PAGEREF _Toc521592835 h 6OTHER USES PAGEREF _Toc521592836 h 64.OPERATION AND APPLICATION OF CRITICAL VALVES PAGEREF _Toc521592837 h 7GLOBE- CONTROL VALVE PAGEREF _Toc521592838 h 7OPERATION PAGEREF _Toc521592839 h 7APPLICATION PAGEREF _Toc521592840 h 75.TYPES OF VALVES PAGEREF _Toc521592841 h 8BALL VALVE OPERATION PAGEREF _Toc521592842 h 8APPLICATION PAGEREF _Toc521592843 h 96.GATE VALVE OPERATION PAGEREF _Toc521592844 h 9APPLICATION PAGEREF _Toc521592845 h 107.CONCLUSION AND RECOMMENDATION PAGEREF _Toc521592846 h 118.REFERENCES PAGEREF _Toc521592847 h 12
INTRODUCTIONOne of the major operations in process industries is the separation of liquid mixtures into their various components. To archive this end, distillation is the most used method, especially in oil refinery industries. The various technological advancements of the distillation columns aim to meet the desire for purer products and great efficiency. CITATION Cou02 l 1033 (Coulson & Richardson, 2002)Distillation is described as a physical process (not a chemical reaction) used to separate a mixture into two or more products that have different boiling points. The primary objective of any distillation column is to separate a feed stream into light-component and heavy-component product streams. The more volatile components of the mixture boil out first in a preferential process.
Distillation columns are used in virtually every process industry. Some of these industries are listed below:
Biofuels or ethanol
Desalination of water
To create liquor, beer or wine
In this report the operation and application of distillation columns is going to be discussed.
OPERATION OF BATCH DISTILLATION UNITS30384753924935Figure SEQ Figure * ARABIC 1: DISTILLATION COLUMNS
Figure SEQ Figure * ARABIC 1: DISTILLATION COLUMNS
30384758667750The greatest distinguishing factor in the batch distillation process is the relative volatilities of components that make up the feed stream. The distillation column is divided into two sections, the top part also known as the enriching section and the bottom part known as the stripping section. When heat is supplied to the column, the more volatile components boil at a lower temperature, thus they are vaporised first, rise to the top of the column, leaving the less volatile components. The overhead vapours are condensed to become liquid again. The contact between the rising vapour and the falling liquid determines the efficiency of the distillation column. For this reason, some of the overhead condensate is refluxed back to the top of the liquid to improve purity of the product. However, it also requires more heat from the re-boiler to re-vaporise the liquid in the reflux stream. It is safe to say that the distillation process is a balancing act between product purity and energy use. This means that for a high purity product to be attained there is need for a high-energy input. CITATION Eme14 l 1033 (Emerson Process Management, 2014). Batch distillation allows for high chemical purity and maximum flexibility. Flexibility in the case of batch distillation means that a single system can separate multiple chemicals with various compositions. This characteristic of batch distillation makes it cheaper as compared to continuous distillation CITATION RCC16 l 1033 (COSTELLO, 2016)It is important to determine, for any given separation, the number of trays required and the flowrates of the liquid and vapour streams. Various methods have been established for the determination of the number of trays this includes LEWIS-SOREL METHOD and McCabe-THIELE METHOD. CITATION Cou02 l 1033 (Coulson & Richardson, 2002)The efficiency of the distillation unit may drop, with corresponding drops in product purity when flooding occurs. Flooding in distillation units means that the amount of vapour rising and liquid falling is too great. Too much re-boil heat and or reflux flow may also trigger flooding. Therefore, there is need for control to ensure that flooding and other quality hindering processes are avoided. The operation of distillation units makes use of various control mechanisms as shown below in figure 2. To ensure that the process runs effectively, control valves are used. Some of the critical valves are discussed below:
Figure SEQ Figure * ARABIC 2: DISTILLATION COLUMN AND CRITICAL VALVES CITATION Eme14 l 1033 (Emerson Process Management, 2014)FEED VALVEFeed valves control the feed going into the column. They are usually set up as flow control loops. An upstream unit or process often controls the valve. Any problem with the feed valve will result in inconsistency in the feed flow. CITATION Eme14 l 1033 (Emerson Process Management, 2014)REFLUX VALVEThe reflux valve usually either a flow or column temperature-control loop. It is used to adjust the purity of the overhead product. The higher the reflux rate, the purer the overhead product will become .However, raising the reflux rate will also require more re-boil heat and eventually will flood the tower. CITATION Eme14 l 1033 (Emerson Process Management, 2014)BOTTOM PRODUCT VALVEThis is typically used to control the level in the bottom of the column. CITATION Eme14 l 1033 (Emerson Process Management, 2014)PRESSURE CONTROL VALVES
Pressure control valves are used to control the column pressure. Higher column pressures will yield better product purities, but require more energy to operate. Normal operating procedure is to minimize the pressure to lower energy costs while maintaining product specifications. There is a low limit because lower pressures reduce the amount of vapour or liquid traffic the column can handle and can make it more likely to flood. CITATION Eme14 l 1033 (Emerson Process Management, 2014)OVERHEAD PRODUCT VALVE
The overhead product valve is typically used to control the level in the overhead receiver .It normally has no effect on column operation unless it causes the level to change quickly and dramatically. CITATION Eme14 l 1033 (Emerson Process Management, 2014)RE-BOIL VALVE
The re-boil valve controls the amount of heat put into the column by the re-boiler. In many cases, steam is used as a heat source. The service is very clean, and fugitive emissions are not a concern. Steam valves are usually very reliable. However, a problematic valve will make the column difficult to control precisely. This will be especially true if the column feed is subject to frequent changes. CITATION Eme14 l 1033 (Emerson Process Management, 2014)TYPES OF TRAYSBesides the use of control valves, the types of trays used for any distillation process are carefully chosen. A tray should provide intimate mixing between the vapour and liquid streams, and that is should suitably handle the desired rates of the liquid and vapour without excessive entrainment or flooding. The three main types of trays are:
The bubble-cap tray (riser/chimney fitted over each hole)
Sieve or perforated tray (perforations covered by lift able caps)
Valve trays (metal plates with holes in them)
In the distillation column operation, the trays play an important role. A summarised sequence is shown below:
The liquid reflux flows across each tray and through of a weir, it enters the down comer.
The down comer extends beneath the liquid surface on the tray below to form a vapour seal
The vapour flows upwards through risers into caps or simple perforations in the tray.
For a given layout of trays, there are certain limits for the flows of vapour and liquid within which stable operations are achieved. It is therefore important to select trays and their layout wisely for better separation. CITATION Cou02 l 1033 (Coulson & Richardson, 2002)
APPLICATION OF DISTILLATION UNITSDistillation units are used virtually in every process industry. The petroleum industry makes more use of distillation units because of the high demand of petroleum products worldwide. Most common industrial applications of distillation units are discussed below.
OIL REFINERYMaking refined oils from crude oil involves the use of distillation columns. Crude oil contains many hydrocarbons that boil at the different temperatures, with different volatilities, thus can be separated from each other. Each hydrocarbon offers various application in chemical industries such as gasoline, plastics, jet fuel, synthetic fibres, kerosene and tyres. CITATION Roy17 l 1033 (Sylvan, 2017)DESALINISING WATERDistillation plants have stopped ‘day zero’ cases in many regions that have deployed water desalination methods using distillation units. These provide effective means to pure water supply, from ocean water. The distillation process remains the same but the methods used to achieve boiling temperatures may differ. The main sources of heat energy for this process are electricity and gas. CITATION Roy17 l 1033 (Sylvan, 2017)DISTILLED SPIRITSWine, beer, liquor undergo through several distillation processes during production. The process is necessary to eliminate any additives and produce a final form of the spirits. The process also removes excess pulp and or grains from the liquid product. CITATION Roy17 l 1033 (Sylvan, 2017)OTHER USESThe pharmaceutical, cosmetic and chemical manufacturing industries depend greatly on distillation. The air separation technology may produce argon, a chemical that can be used to protect the filament in the light bulbs and provide glow in fluorescent tubes. CITATION Roy17 l 1033 (Sylvan, 2017)OPERATION AND APPLICATION OF CRITICAL VALVESControl valves are very important in any process where fluid flow is monitored and manipulated. A basic valve permits or restricts fluid flow at a set time and or adjust the pressure of the system accordingly. A complete control valve consists of the valve itself, an actuator and a valve control device when necessary. An actuator provides the operation force of the valve i.e. it aids with the opening and closing mechanism. The valve control device ensures correct operation conditions concerning interpretation and manipulation. CITATION Kat07 l 1033 (Katzman, et al., 2007)GLOBE- CONTROL VALVEOPERATION
A globe valve is a type of valve used for regulating flow in a pipeline. It consists of a movable disk-type element and a stationary ring seat in a generally spherical body. The valve can have a stem or a cage, similar to ball valves, that moves the plug into and out of the globe. The fluid’s flow characteristics are controlled by the design of the plug being used in the valve. A seal stops leakage through the valve. One of the most important advantage that globe valves have is that they are easily maintained. They usually have a top that can be easily removed, exposing the plug and seal. Globe valves are good for on, off, and accurate throttling purposes but especially for situations when noise and cavitation are factors.
Best shut off and regulation
Used for throttling applications
High pressure drop i.e. head loss
APPLICATIONListed below are some typical uses of globe valves:
Cooling water systems
Turbine deals and drains
Fuel oil system where flow is regulated and there is high importance of leak tightness
High point vents and low point drains where safety is of high importance.
Chemical feed, feed water, extraction drain systems. CITATION Pip13 l 1033 (Piping Guide, 2013)TYPES OF VALVESBALL VALVE OPERATIONA ball valve has a spherical disc, the part of the valve, which controls the flow through it. As the name suggests, ball valves are stop valves that use a ball to stop or start the flow of fluid. The sphere has a hole, or port, through the middle so that when the port is in line with both ends of the valve, flow will occur. When the valve is closed, the hole is perpendicular to the ends of the valve, and flow is blocked. CITATION Kat07 l 1033 (Katzman, et al., 2007) .When the valve handle is operated to open the valve, the ball rotates to a point where the hole through the ball is in line with the valve body inlet and outlet. A complete shut requires only a 90° rotation of the hand-wheel for a total shut off. This characteristic minimizes leakage due to gland seal wear and tear.
A ball valve is generally the least expensive of any valve configuration
has low maintenance costs
Quick, quarter turn on-off operation, ball valves are compact, require no lubrication, and give tight sealing.
Conventional ball valves have relatively poor throttling characteristics
In a throttling position, the partially exposed seat rapidly erodes because of the impingement of high velocity flow.
APPLICATIONBall valves are usually recommended only for use in fully closed or fully open position. The flow cannot be regulated by partially opening or closing the valve. CITATION Meg15 l 1033 (MegaDepot, 2015)Steam service
Vacuum application s requiring bubble-tight services
Instrument root valves
Cooling water and feed water systems
GATE VALVE OPERATION
Industrial piping configurations often include gate valves. Gate valves have less obstruction to flow, less turbulence and less pressure drop within the valve. The wedge is entirely lined out of the waterway when the valve is completely open. This set up provides a straightway flow area through the valve. CITATION Meg15 l 1033 (MegaDepot, 2015)ADVANTAGES
Gate valves provide a tight seal when closed.
Used for a wide variety of fluids.
They are bidirectional
Not suitable for throttling processed
When partially open, it is prone to vibration
Repairs more difficult to accomplish
APPLICATIONGate valves are widely used as socket or butt-welding end-gate valves in:
Feed water pipes
Water piping or water distributing pipes
CONCLUSION AND RECOMMENDATIONThe research findings showed that product purity/quality and high cost are inseparable. The distillation process has brought about diversity in process industries.
It is a highly important decision to choose the right distillation method. This includes conducting research on the components involved. For a large amount of flexibility, batch distillation is ideal, but it comes with a high risk of contamination. While continuous distillation is more expensive than batch distillation, it offers better quality with its highly efficient process. It is therefore very important to attain as much information about the components involved as possible.
REFERENCES BIBLIOGRAPHY COSTELLO, R., 2016. Batch vs. continuous distillation. Online Available at: rccostello.com/wordpress/distillation/batch-vs-continuous-distillation/Accessed 09 August 2018.
Coulson ; Richardson, 2002. Particle technology and separation processes. In: Harker, ed. Chemical Engineering. Oxford: Elsevier, p. 542.
Emerson Process Management, 2014. Control Valves. In: Chemical Units. dubai emirates: fisher controls international, pp. 3-4.
Katzman, D., Moreno, J., Noelanders, J. ; Winston-Galant, M., 2007. Valves. In: Chemical process dynamics and control book. Michigan: University of Michigan, pp. 334-356.
MegaDepot, 2015. A guide to types of valves. Online Available at: https://megadepot.com/resource/a-guide-to-types-of-valvesAccessed 08 August 2018.
Piping Guide, 2013. globe valve types, construction , application and advantages. Online Available at: www.pipingguide.netAccessed 8 August 2018.
Sage, B. T. V., 2016. Different Valve types, application and suitability. Online Available at: https://www.linkedin.comAccessed 01 August 2018.
Sylvan, R., 2017. what are the uses of distillation in industry?. Online Available at: http://bizfluent.com/about-5941994-uses-distillation-industry-.htmlAccessed 01 August 2018.