Brief review about the production process & Prospectus of the Transformer oil In Asia .

Brief review about the production process & Prospectus of the Transformer oil In Asia .

K.K.Dhar* , A.K. Das,**

Dipartimento di Chimica Materiali Ingegneria Chimica “Giulio Natta”, Politecnico di Milano,

via Mancinelli 7, 20131 Milano, Italy

*kdhar@chem.polimi.it kalyan.dhar@mail.polimi.it

** Professor Department of Applied chemistry & Chemical Engineering University of Dhaka , Dhaka-1000, Bangladesh

Keywords: Oil , Petroleum oil , Highly refined oil .

Abstraction:

Transformer oil forms a very significant part of the transformer insulation system and has the important functions of acting as an electrical insulation as well as a coolant to dissipate heat losses.  

A transformer is a device with two or more stationary electrical circuits that are conductively disjointed but magnetically coupled by a common time varying magnetic field. Transformers are basically passive devices for transforming voltage and current. One of the windings, generally termed as secondary winding, transformer energy through the principle of mutual induction and delivers power to the load. The voltage levels at the primary and secondary winding are usually different and any increase or decrease of the secondary voltage is accompanied by corresponding decrease or increase in current.

A transformer oil has to provide the necessary electrical insulation and at the same time act as a medium for the transfer of heat energy form the core and winding of the transformer.

HISTORY OF TRANSFORMER OIL

The dielectric constant of transformer oils is about 2, and depends on oil composition, being rather higher for more aromatic oils. The basic raw material for the production of transformer oil is a low viscosity lube termed as transformer oil base stock (TOBS), which is normally obtained by fractional distillation of crude petroleum and subsequent treatment of fractions. Important characteristic of TOBS (given in table 1) must be kept within permissible limits in order to produce good insulating oils. TOBS is further refined by acid treatment process to yield transformer oil.

TABLE : 01 (CHARACTERISTIC OF TOBS)

SL No.	Characteristic	Requirement
1	Viscosity at 37.8oC	58-86 Sec.sus
2	Pour point. max	-12oC
3	Flash point. min	140oC

            Again transformer oil consists of four major generic class of organic compounds, namely, paraffins, napthenes, aromatics and olefines. All these are hydrocarbon and hence insulating oil is called a pure hydrocarbon mineral oil.

            For good fresh insulating oil, it is desirable to have more of saturated paraffins, less of aromatic and napthenes and none of olefines. However for better stability of properties, it is necessary to have optimum aromatic and napthenic hydrocarbons. Such an optimum balance is struck by a carefully controlled refining process. Depending upon the predominance, oil is usually term as of paraffinic base or napthenic base.

TABLE : 02 SCHEDULE OF CHARACTERISTIC OF INSULATING/TRANSFORMER OIL

SL No.	Characteristic	Requirement as per is 335-1983
1	Density at 27oC, max	0.89g/cm3
2	Kinematic viscosity at 27oC, min	27cst
3	Interfacial tension at 27oC min	0.04 N/m
4	Flash point, min	140oC
5	pour point, max	-9oC
6	Neutralization value (total acidity) max	0.03 mgKOH/g
7	Corrosive sulphur	non-corrosive
8	electric strength (breakdown voltage) min a) As received b) After filtration	30 KV (rms) 50 KV (rms)
9	Dielectric dissipation factor (tan-delta) at 90oC, max	0.005
10	Specific resistance (resistivity), min  a)      At 90oC b)      At 27oC	30´1012Wcm. 500´1012Wcm

PHYSICAL PROPERTIES OF TRANSFORMER OIL

1. Density : This test has special significance when transformer is operated in a very low temperature zone. The maximum value of density fixed at 27^oC ensures that water in form of ice present in oil remains at the bottom and does not tend to float on the oil are up to a temperature of about -10^oC.
2. Flash point : It is the temperature at which oil gives so much vapour that this vapour, when mixed with air, forms an ignitable mixture and gives a momentary flash on application of flame under prescribed condition. A minimum flash point is specified in order to prevent the risk of fire that might result by accidental ignition.
3. Viscosity : It is a measure of oil resistance to continuous flow without the effect of external forces. The oil must be mobile, as heat transfer in transformers occurs mainly by convection currents, since viscosity increases with decreases in temperature, it is necessary that viscosity be as low as possible at low temperatures.
4. Pour point : The temperature at which oil will just flow under the prescribed conditions is known as the pour point. If the oil becomes too viscous or solidifies, it will hinder the formation of convection currents and thus cooling of equipment will be severely affected.
5. Moisture content : The amount of free and dissolved water present in the oil is its moisture content and is expressed in ppm ( parts per million by weight  i.e. mg/kg). Presence of moisture is harmful since it adversely affects the electrical characteristics of oil and accelerates deterioration of insulating paper.
6. Interfacial tension (IFT) : This is a measure of the molecular attractive force between oil and water molecules at their interface. This test provides a means of detecting soluble polar contaminants and products of deterioration, which decrease molecular attractive force between oil and water. It  is considered that IFT gives an indication of degree of sludging of oil.

ELECTRICAL PROPERTIES OF TRANSFORMER OIL

1.      Electric strength (breakdown voltage) : Breakdown voltage is the voltage at which breakdown occurs between two electrodes when oil is subjected to an electric filed under prescribed conditions. Electric strength is the basic parameter for insulation system design of a transformer. It serves to indicate the presence of contaminating agents like moisture fibrous materials, carbon particles, precipitable sludge and sediment.

2.      Resistivity (specific resistance) : This is the most sensitive property of oil requiring utmost care for its proper determination. Resistivity in ohm is numerically equivalent to the resistance between opposite faces of centimeter cube of the liquid.

Insulation resistance of winding of a

transformer is also dependent upon the resistivity of oil. A low value indicates the presence of moisture and conductive contaminates. 

3.      Di-electric dissipation factor (DDF) : DDF is numerically equal to sine of the loss angle (approximately equal to tangent of loss angle for dielectrics) and is a good tool to indicate the quality of an insulation. A high value of DDF is an indication of the presence of contaminates as deterioration products such as water, oxidation products, metal soaps, soluble varnishes and resins.  

CHEMICAL PROPERTIES OF TRANSFORMER OILS

1. Oxidation stability : This is the measure of neutralization value and sludge after oil is aged by simulating the actual service conditions of a transformer.

The oxidation stability test is very important for

new oil but not for oil in service and shows the presence of natural inhibitors which impart antioxidation characteristics to oil.

2. Corrosive Sulphur : Crude petroleum usually contains sulphur compounds, most of which are removed during the refining process. This test is designed to detect any traces of free corrosive sulphur that may be present in oil. Presence of corrosive sulphur in oil will result in pitting and black deposit on the surface of bare copper used in transformer, which will adversely affect the dissipation of heat and consequently performance of the equipment.
3. Sediment and precipitable sludge : These are oil deterioration products or contaminants which are insoluble after dilution of the oil with n-heptane under prescribed conditions. However, precipitable sludge is soluble in the solvent mixture of equal parts of toulene, acetone and alcohol but sediment is insoluble in this solvent mixture. These contaminants are determined for oils in service. Oil is considered unsatisfactory for use if sediment or precipitable sludge is detected.

    

4. Neutralization value (total acidity) : It is a measure of free organic and inorganic acids present in the oil and is expressed in terms of milligrams of KOH required to neutralize the total free acids in one gram of oil.

Oxidation of oil in service is a consequence of reaction between hydrocarbons present in the oil and oxygen. The oxygen may be atmospheric since oil comes into contact with the atmosphere air during breathing of transformer, or may have been dissolved in oil if oil is not designed properly, or may be liberated due to effect of heat cellulose insulation.

Oxidation of oil is a chain reaction by which organic acids and sludge are formed. Copper present is a large quantity in transformer acts as a strong catalyst in oxidation.

Hence, as far as possible, no bare copper is allowed to be used in power transformers. The product of oxidation are injurious to the insulation system of transformer. Acids formed give rise to formation of sludge which precipitates out and deposits on windings and other parts of transformer.

Acids formed give rise to formation of sludge which precipitates out and deposits on windings and other parts of transformer. This causes hindrance to proper oil circulation and heat dissipation. The acids also encourage deterioration of cellulose insulation i.e. paper, pressboard and wood. Water is produce during oxidation which reduces electric strength of oil and also accelerates corrosion of metals and deterioration of insulating materials.

Hence the measurement the total acidity is the most convenient and direct method of accessing the capability of oil for non-formation of acids during service.

PRODUCTION AND REQUIREMENT OF TRANSFORMER OIL IN BANGLADESH

REQUIREMENT OF TRANSFORMER OIL IN BANGLADESH

SOURCE : RURAL ELECTRICAL BOARD (REB)

Capacity of transformer	No. of phases (j)	No. of Transformer	Weight of oil per transformer (in kg)	Amount of oil (in kg)
10 MVA	3j	12	4,000	48,000
5MVA	3j	20	3,000	60,000
3.33MVA	1j	32	2,000	64,000
1.67 MVA	1j	40	1600	6400
100KVA	1j	200	110	22,000
75KVA	1j	500	95	47500
50KVA	1j	1000	85	85000
37.5KVA	1j	1800	75	135000
25KVA	1j	3500	65	227500
15KVA	1j	10000	45	45000
10KVA	1j	30000	30	300000
5KVA	1j	24000	22	528000
Total				1568400 kg

Total amount of transformer oil required (REB) in (2003-2004 year) = 1568400 kg = 1568 T

SOURCE : POWER DEVELOPMENT BOARD  (PDB)

Requirement for year	Materials (Transformer oil)	Requirement of supply zone	present storage	Total amount of transformer oil	Cost of transformer oil
					Total cost	Unit cost
2004-05	Do	2500 Drum	47 Drum	10,0000	75,00000	75/=
2003-04	Do	-	500 Drum	20,0000	15,000000	75/=
2002-03	Do	-	2000 Drum	2,00000	15000000	75/=
2001-02	Do	-	-	50000	3750000	75/=

            So from the above data we can easily calculate that the total demand of transformer oil in our country (2003-2004 year) = 2000 tone/year. 

            \ Total demand per year : 2000 tone/year.   

LITERATURE SURVEY

The chemical structure of transformer oil : Transformer oils are obtained by processing petroleum. Petroleum differs in chemical composition according to its source. This also applies to its products, especially to transformer oils. It has been found in practice that the service properties of the oils depend both on their origin and on their production method, and that there is a certain relationship between the chemical composition of transformer oils and their service properties.

A) Hydrocarbon constituents of transformer oil : The hydrocarbon compound which  constitute the major part of the oil, can be divided into three main groups :

                                                              i.      Paraffins

                                                            ii.      Napthenes

                                                          iii.      Aromatic compounds.

i) Paraffins : Paraffins are saturated hydrocarbon with a straight chain (normal paraffin in fig (i) or a branched chain (iso paraffins) in fig (ii) without any cyclic structure

 

ii) Napthenes : Cyclo paraffin or alicyclic compounds (populary called napthenes) are saturated hydrocarbons containing one or more five-or-six-membered rings. Eaxh of these rings may have one or several straight or branched side chain, depending on the number of rings, napthenes are monocyclic (iii), bycyclic (iv) and so on.

 

iii) Aromatic hydrocarbons: Aromatic hydrocarbons contain one (v) or several aromatic rings which may be combined with alicyclic rings; the rings may or may not be alkyl chains and/or paraffin side chains. The aromatic nuclei may be condensed as in napthalene and phenanthrene (vi) or isolated (vii). A mixed alicyclic aromatic hydrocarbon is shown structure (viii).

 

Unsaturated hydrocarbon (hydrocarbons having one or more olefinic bonds) are not usually found in transformer oil prepared from straight run distillation products of petroleum.  

B) Non hydrocarbons constituent of transformer oils : The non hydrocarbons constituents of transformer oils comprise tarry asphaltic substances, sulphur and nitrogen containing organic compounds, napthenic acids, esters, alcohol and organometallic compounds.

i) Tars : During purification of transformer oil distillates a large amount of tars is removed. Their content is the final treatment oils does not as a rule exceed 2-2.5%. The tars have been classified as follows :

a.       Neutral tars

b.      Asphaltenes

c.       Carbenes

d.      Asphaltogenic acids and their anhydrids.   

ii) Sulphur compounds: Sulphur compounds are present in all petroleum crudes. Their amounts however very from less thanb 1 to 20 wt/. They have a considerable influence on the properties of the petroleum and determine which treatments are used in its processing.

The  main group of sulfur compounds of petroleum are as follows.

a.       Mercaptans (thiols)

b.      Sulfides (thia alkanes)

c.       Disulfides (dithia alkanes)

d.      Thiophenes

iii) Nitrogen compounds :

iv) Napthenic acids and other oxygen containing compounds

v) Metal containing compounds

C) PRODUCTION OF TRANSFORMER OILS : Transformer oil are produced by refining petroleum distillates which boil between 300 and        400^o C at atmospheric pressure.

Classification of production :

            Transformer oils made from petroleum are classified in accordance with the methods of refining the distillate :

1)      Acid-alkaline purification.

2)      Selective solvents extraction.   

3)      Deparaffination.

4)      Contact purification using adsorbents.

5)      Hydrogenation under pressure.

A combination of two or more of these methods is generally used.

Industrial refining method:

            The purpose of refining the oil is the removal of undesirable constituents which adversely affect its stability to oxidation, its electrical insulating properties, and its low temperature fluidity. These undesirable constituents include unsaturated hydrocarbons, nitrogen compounds, some sulfur compounds, tars, polycyclic hydrocarbons with short side chains and solid hydrocarbons (particularly paraffin and mineral waxes)

The  industrial refining methods are briefly summarized hereunder:

1) Acid-alkaline purification :

Principle: Acid-alkaline purification is essentially the treatment of the distillate by 93-98% Sulfuric Acid (followed by washing with aqueous alkali). The amount of acid used depends on the chemical composition of the raw materials and the degree of refining required, and varies between 5 and 20%.

But the disadvantage of purification with sulfuric acid are as follows :

a)        The acid is insufficiently selective; together with the undesirable constituents removed, valuable constituents are also entrained by the sulfuric acid sludge, while some sulfur compounds and mixed alicyclic aromatic substances are incompletely removed.

_b)          The sludge formed is useless, its removal is complicated and expensive, and reservoirs are necessary for its storage.

c)        These drawbacks as well as the necessity of increasing the production of transformer oils by using less suitable raw materials led to the development of new methods.

2) The selective solvent extraction :

Principle: The selective solvent extraction of undesirable componenets from the distillate is based on the differences in solubilities between the individual classes of chemical compounds in the distillate.

            Phenol is mostly used at present for the production of transformer oils from sulfur containing crudes. In the order of decreasing solubility in phenol the constituents of transformer oils can be arranged as follows : tars, sulfur and nitrogen compounds, polycyclic aromatic hydrocarbons, and finally napthenes and paraffin hydrocarbons.

            In order to increase the selectivity of phenol, 3-7% water is added. The yield of the refined oil depends on the quality of the raw material and the amount of phenol used; it averages about 70%.

Process description :

            In fig (1) extract stripper steam and some other vapours are sent through an absorber held at 225 to 245^o F wherein the incoming charge absorbs phenol from the stripping steam. Total losses of phenol are said to be under 0.04% of the phenol circulated.

The operation steps are as follows :

a.       Heated lubricating oil-stock absorbs phenol from steam, etc (mainly extract and raffinate stripping steam) at about 235^o F. Stock is cooled and contacted with phenol in a counter current extraction tower. The bottom of the tower is cooled to about 110^o F with phenolic water for distillate stocks or 155^o F for residual stocks and the top is kept warm (150^o F for distillate and 230^o F for residual stocks) by hot phenol.

b.      The valuable raffinate (about 20% phenol) is heated to about 550^o F and flashed at atmospheric pressure and it then flows downward into a vacuum fractionation and steam stripping tower (22 in mercury vacuum) for the removal of phenol down to about 0.001%.

c.       The low viscosity index extract when operating on a pennylvania stock contains about 85% phenol and 8% water. Phenolic water is removed from it by heating to about 650^o F and fractionating in the small tower situated above the phenolic water tower. It passes to storage through a steam stripper which reduces the phenol to about 0.005%.         

3) Deparaffination:

Principle : The solid hydrocarbons are not removed by any of the other refining processes (acid-alkali, phenol, hydrogenation or adsorption). Moreover, as a result of the removal of about 30% of the tars and aromatic hydrocarbons, the concentration of the solid hydrocarbons (mainly paraffins) increases. 

            The refined transformer oil after treatment with phenol has a solidification point of 20^o C. The introduction of additives does not decrease the solidification point. In order to separate the solid hydrocarbons the oil is treated with a solution containing methyl ethyl ketone (MEA).

            This is followed by thermal treatment at 50-70^o C  i.e. 25-30^o C higher than the cloud point of the oil, cooling to the temperature required                        (-55-60^o C), and finally separation of the solid hydrocarbons by vacuum filtration or centrifuging.

            It has been proposed that activated charcoal be used for deparaffination, since unlike silica gel, alumina gel or bleaching clays, it can adsorb on its surface hydrocarbons with long, almost unbranched chains (mainly solid normal) paraffins.  

Essential equipments : According to Ebner and Mertens the essential equipment for an MEK deparaffination plant consists of seven major sections :-

a)      Direct-expansion ammonia chillers.

b)     Double-pipe scrapped surface exchangers for both solvent dewaxing and wax recrystallizing process sections.

c)      Continues dewaxing filters.

d)     Tubular exchangers to chill wash solvent.

e)      Flue gas generation, circulation and chilling.

f)       Products recovery system for dewaxed oil, slack wax, slop wax filtrate, product wax.

g)      Solvent water separating and recovery system.

Process description : A flow diagram of the MEK process is indicated in fig (2). The wax bearing oil and the solvent streams are mixed under control of a ratio flow controller. The oil solvent stream flows through exchangers and chillers, from which it emerges at a controlled temperature which is maintain by regulating the pressure on the refrigerant side of the charge mix chiller. 

            The liquid phase of the charge to the filters is adjusted to the proper filtration viscosity by the addition of chilled solvent to the chilled oil solvent mixture.

Recovery of solvent from the wax cake is accomplished in a manner similar to that from the filtrate, except that any water inadvertently entering the oil or solvent side of the dewaxing system quickly finds its way as ice into wax cake. To remove this water, the wax cake is heated before evaporation of solvent to a controlled temperature of about 130^o F at which the water readily forms a separate layer.

Several stocks are usually dewaxed in a single plant using a single solvent mixture and accordingly the proper amount of solvent for each stock must be determined.

4) Contact purification (Clay treatment):

Principle : In this method, the oil is mixed with bleaching earth (clay), subjected to heating until absorption is completed and finally filtered to remove the clay from the oil. The bleaching earths usually contain aluminum hydrosilicates. The adsorptional properties of the clays depend not only on the chemical composition but also on the structure of the particles, pore diameter, moisture content and particle size.

Process description :

            Thermofor continuous percolation process (clay process) is a continuous regenerative process for stabilizing and decolorizing lubricants or waxes that have been distilled, solvent refined or acid treated (in fig-3). The charge stock in heated to 50-175^o C, injected into the base of a clay filled tower and allowed to percolate in countercurrent flow through the bed. Spent clay is continuously withdrawn from the base of the tower; regenerated clay is added to the top of the bed to maintain a constant level. 

5. Refining by hydrogenation (treatment with hydrogen)

Principle : In contrast to the methods mentioned above, this process is based on a chemical conversion of the hydrocarbon and sulfur compounds contained in the transformer distillates.

            This is the main distinction and advantage of this method. In the production of transformer oils, hydrogenation of the distillates is followed by distillation  of the hydrogenated product, deparaffination and contact or percolation purification with an adsorbent. 

SELECTION OF TECHNOLOGY FOR PRODUCTION OF TRANSFORMER OIL

            In recent years there has been a growing tendency to use low-viscosity transformer oils in order to improve the cooling properties of transformer. This is achieved by narrowing the fractional composition of the oil while somewhat lowering the flash point.

            Special attention is devoted to improving the insulating properties of the oil i.e. to decreasing tand, the tangent of the dielectric loss angle, to decrease the hygroscopicity and to increasing the gassing resistibility of the liquid dielectric under the influence of corona. The decrease in tand is attained by through adsorptional contact purification; this is an essential final step in the polishing of the oil.

            The hygroscopicity of the oil is decreased by lowering the level of polaradmixtures and aromatic hydrocarbons; it should be noted, however, that the latter impart a high gassing resistibility to the oils. The chemical stability is a basic service index of transformer oils. In this respect a very high level a tars and aromatic hydrocarbons, especially polycyclics with short side chains, is undesirable since they tend to form deposits under the conditions in which transformer oil is used.

Taking into account these incompatible requirements with respect to chemical properties, the following choices are available in the production of transformer oils from petroleum.

1) Production of oil with optimum chemical composition by means of comparatively mild acid-alkali treatment, selective (solvent treatment) or adsorptional refining.

            Because of the increasingly strigngent requirement, the production of a suitable oil in this way becomes an increasingly difficult task, which can only be solved by using high quality crudes as raw material. An improvement in the properties of such oil can be achieved by adding antioxidants, though it should be borne in mind that an oil which has not been intensively refined absorbs only slightly the standard additives or those now being investigated.

2) Production by the same methods of oils refined to higher degree :

            The stability and gassing resistibility of oils can be increased to the necessary level  by means of special additives such as antioxidants and substances which increase the gassing resistibility under electrical stress. This method can be used in processing lower-quality crudes.

3) Production of oils by methods making it possible to change at will  the chemical structure of its constituents:

         This trend includes destructive hydrogenation. The permissible concentration of sulfur in transformer oils is a serious problem. It is known that some sulfur compounds are inhibitors of oxidation and can passivate metals.

            It has been shown that concentrates of sulfur containing sulfur compounds isolated from distillates are inhibitors.  On the other hand,  organic sulfur compounds which do not contain sulfides do not inhibit the oxidation process.           It was experimentally proved that when a distillate of a sulfur containing crude is purified with phenol, the oil with 0.3-0.4% sulfur is the most stable. On the other hand, it has been claimed that the higher the sulfur level in an oil refined with phenol, the higher its stability; in any case the sulfur  concentration may be as high as 1%.

            In selective (solvent) refining of a distillate of sulfur containing crudes the sulfur compounds are extracted together with the tars and the aromatic hydrocarbons. Therefore the level of sulfur in an oil indicates the degree of refining.  Thus the optimum degree of refining of an oil without added inhibitors is indirectly determined by the sulfur content; a higher susceptibility of the oil to the action of antioxidants is attained by a higher degree of refining i.e. a lower sulfur content.

           

Phenol refined oil containing 1% sulfur is unstable both in the pure form and with up to 0.7% Ionol (butyalated cresol mixture) additive. An oil containing 0.4-0.6% sulfur inhibited by 0.2-0.3% Ionol is satisfactory generally the upper limit of sulfur content in the oil is considered 0.6%.

           

Thus, based on the above discussion and also considering the cost effectiveness in the context of Bangladesh, the following general scheme for production of transformer oil, from vacuum distillate (fraction 300-400^o C), consisting of three treatment processes e.g. phenol solvent extraction, MEK deparaffination and clay treatment is selected.  

ADDITIVES FOR IMPROVING QUALITY AND SERVICE LIFE OF TRANSFORMER OIL

            The following additives are used industrially for the stabilization of transformer oils:-

        i.      Phenyl-b-napthylamine (PBN)

      ii.      2,6-di-tert-4-methylphenol (DBPC) (trade name include Ionol, Topanol-0, and vianol, and 2,4-dimethyl-6-tert-butylphenol,

These additives are introduced into the oil in amounts ranging from 0.1-0.5%. For regenerated oils the concentration of additives may be increased to 1%.

In many countries, Ionol, p-hydroxydiphenylamine and pyramidene are used for these purpose. The most widely used additives is Ionol. Because-

1.                             It can almost completely prevent the formation of precipitates in thoroughly purified oils ; the oxidation products are soluble in the oil.

2.                             The additive readily dissolves in the oil the even when highly concentrated .

3.                             The use of Ionol in oils purified by phenol from sulfur containing crudes.

The only drawbacks of Ionol is  the fact that it must be added to the oil in large amount (0.2-0.5 wt%) like most additives, Ionol is effective in inhibiting the oxidation of oils which have been extensively purified.

MAJOR EQUIPMENTS AND MACHINERIES REQUIRED

1.	Extraction (Solvent) tower.
2.	Continuous vacuum filter for MEK Deparaffination.
3.	Extract stripper for phenol treatment.
4.	Absorber (Phenol). For water elimination.
5.	Phenol storage tank.
6.	Treating tower for phenol treatment.
7.	Raffinate tower (phenol)
8.	2 coil stil (phenol)
9.	Water and phenol tower.
10.	Ketone fractionator.
11.	Surge tk. for MEK Deparaffination.
12.	Accum Tank (MEK).
13.	Flash tank (MEK).
14.	Wax storage tank
15.	Feed tank for MEK Deparaffination.
16.	Receiver tank (MEK)
17.	Settling tank (MEK)
18.	Foam trap tank (MEK)
19.	Dewaxed oil stripper.
20.	Wax stripper
21.	Clay burning kiln and drier.
22.	Percolator for clay treatment.
23.	Washer for clay treatment.
24.	Extract tower.

 

The Principle scheme of this extraction tower is hereunder:

1- Phenol – water inlet 2- Feed (Fr. 300-4000c) inlet 3- Cold Recycle inlet 4- Extract outlet 5- Hot Recycle stream outlet

6- phenol inlet 7- Raffinate outlet 8- Safety valve 9- Distributors 10 -Level indicators

						III
			I
									IV
									IV
										IV
							II

The Principle scheme of this multistage extract stripper represented as:

I-       Raw-extract inlet.

II-    Product –extract outlet

III- Vapor outlet

IV- Steam

PROCESS CONTROL AND QUALITY CONTROL OF TRANSFORMER OIL

Various process control and quality control are operated to get the desired products with desired quality. The process control ensures the continuation of the process. For the control of process the industry required a control room from which an operator can easily control of the process temperature and pressure within the desire range.

On the other hand, the quality control ensure, the product quality and the inspection decides whether the certain item or production meets the requirements or not. This is done in a laboratory. The process comprises of the following steps.

Raw material Section:

Before the preparation of the feed stock raw materials are analyzed to check the required quality.

Product testing:

Before final delivery of the product it is tested to check density, activity, composition etc, so that it attains the market demanded quality. In case of inferior products, it is recycled to the process.

Materials of construction:

In the selection of material for the construction of material for the construction of a chemical unit, resistance to the corroding medium is usually the determining factor. Other important factors are elevated temperature and pressure. The choice of material and its stability in the presence of transformer oils is of great importance and essential for safe handling of transformer oil.

The temperature of the transformer is directly connected with the life of the insulating materials, and so careful attention is necessary. The maximum temperature allowed for the oil is 90⁰c in case that the oil comes is contact with the air and 95⁰c in case that the oil is out of contact with the air when the ambient temperature is 40⁰c.

The oil level has always to be checked from the view point of insulation and cooling.

The Dialectic Strength of transformer oil:

The Transformer is a main part that insulates the transformer and lowering of its dielectric strength means lowering of dielectric strength of the transformer itself therefore this must be carefully inspected. The dielectric strength of oil has been standardized above 30 kv at 2.5 mm sphere gap, if the strength is lower refinement or new oil filling is necessary.

The dielectric strength is also subject to moisture and foreign materials contained in the oil. In measuring the dielectric strength, the fluctuation of the measured values will be so large that they become unless sampling of the oil be done with care and a proper method of test be selected.

Storage and shipment:

The storage is done by using stainless steel storage tanks. Small amount of transformer oil are shipped in steel cylinders, large amount of transformer oil has been transported by rail in tank cars of 36 and 107 m³ capacity.

MATERIAL BALANCE FOR PRODUCTION OF TRANSFORMER OIL

Production capacity 2000 MT/Yr,

Transformer  oil stream days- 330

1. Material balance for phenol solvent extraction

Input				Output
Material	MT/year	Kg/day	%	Material	MT/year	Kg/day	%
Vacuum distillate (fraction 3000-4000c)	4880	14787.88	100.00	Raffinate	2930	8878.79	60.00
Phenol	(9760))			Extract	1950	5909.09	40.00
TOTAL	4880	14787.88	100.00		4880	14787.88	100.00

2. Material balance for MEK  Deparaffination

Input				Output
Material	MT/year	Kg/day	%	Material	MT/year	Kg/day	%
Raffinate from solvent extraction	2930	8878.78	100.0	Dewaxed oil	2050	6212.12	70.00
Solvent (MEK)	(8790)			Slack wax	880	2666.66	30.00
TOTAL	2930	8878.78	100.00		2930	8878.78	100.00

3. Material balance for clay treatment

Input				Output
Material	MT/year	Kg/day	%	Material	MT/year	Kg/day	%
Dewaxed oil	2050	6212.12	100.0	Transformer oil base stock (TOBS)	1940	5878.78	94.6
(Clay)	(123)		(6.0)	Loss of oil with clay	110	333.33	5.4
TOTAL	2050	6212.12	100.0		2050	6212.12	100.0

4. Material balance for compounding

Input				Output
Material	MT/year	Kg/day	%	Material	MT/year	Kg/day	%
Transformer oil base stock (TOBS)	1940	5878.78	99.7	Transformer oil	2000	6060.61	100
Additives	60	181.82	0.3
TOTAL	2000	6060.61	100.0		2000	6060.61	100.0

ENVIRONMENTAL POLLUTION, HAZARD AND SAFETY ASPECTS

Environmental pollution is one of the most vital problems faced by human being. To some extent, environmental pollution is an inescapable by product of industrial development. There are many kinds of environmental pollution such as air pollution, water pollution, land pollution, noise pollution etc.

Considerable pressure has developed in recent years from the EPA and similar to discontinuous disposal of waste transformer oil in streams, chemical dumps and other environmental channels. The problem has been highlighted by possible health hazards resulting from the presence of aromatic hydrocarbons as well as sulfur, chlorine, and other additive materials of questionable toxicity in the oils.

Although most of the constituents of transformer oil  are not, or only slightly, soluble in water, some of the additives and some of the organic constituents can be dissolved in water to a certain extent. These components can easily infiltrate into soil to reach the aquifer. The transfer of the main components of  aliphatic structure takes much longer, but then leads to long term contamination, because of their chemical stability and persistence in biological system.

a.      Direct effects:

The most obvious and evident effects of pollution caused by used oil dumped into aquatic systems are the well known specific effects on water surface. Due to its density, oil covers the surface of water, while the biodegradation of most of its component is very low, spilled oil remains for a long this in ecosystems; the oil layer on water surface decreases solar radiation into the water, as well as oxygen supply through water surface, resulting in considerable reduction of biological activity. Oily particles with an increased density sink to the bottom, where they affect plant growth. large amounts of oil, accumulated on the bottom of an aquatic system can destroy aquatic life completely.

Burnt used oil causes air pollution, related to the released toxic inorganic and organic compounds. Human health as well as flora and fauna are directly affected by co, so_x, No_x, soot particles and many other pollutants.

b.       Indirect effects:

In addition to the direct impact on plants, either in terrestrial or aquatic systems, the negative effect on plant growth or the biological activity of soils encourage denser vegetation and increases erosion, on slopes as well as along river banks.

The extreme stability and chemical properties of oil constituents promote accumulation in fat tissues, leading to considerable levels of concentration at the end of the chain. The indirect effect is used. Transformer oil which is discharged in the environment in an uncontrolled way can exceed the direct ones by far, it spilled oil reaches the ground water.

 Pollutants, released to air where used oil is burnt under improper and unsuitable conditions, can affect systems in the long term due to the extreme persistence and high transfer rates of some of the released organic compounds or heavy metals to organic structure. 

Preventive measures:

 Risk avoidance by general preventive design measures, as well as reactive fire. In safety concepts, distinctions are made between primary, secondary and tertiary measures. Primary safety precautions aim at the exclusion of causative risks such s leakage, formation of explosive mixtures by proper conceptual design. Secondary measures consist mainly in the avoidance of ignition sources of any kind (electro-statically or mechanically generated sparks). Tertiary measures should minimize dangerous results in case fire or explosion relief systems and suitable fire extinguishing systems.

Protective equipment for handling transformer oil:

(a)    Eyes: wear chemical type’s goggles or face shield (optional).

(b)   Skin: Exposed employees should exercise reasonable personal cleanliness; this includes cleaning exposed skin areas several times daily with soap and water and laundering or dry cleaning soiled work clothing at least weekly.

(c)    Respiratory: None required if exposures are within permissible concentrations.

Special precautions:

(a) Storage:

             I.      Minimum feasible handling temperatures should be maintained.

          II.      Periods of exposure to high temperature should be minimum.

(b) Handling: Water contamination should be avoided.

(c) Ventilation: Normal.

(d) Unusual fire Hazards: Avoid heat sources, open flames and other sources of ignition.

Safety Regulations:

Regulations (mandatory) and standards (mandatory or non mandatory) apply for the safe production, storage and handling of transformer oil. They are mostly concerned with transpiration; other operations are covered by more general regulations. Excellent listings are given for the United States and for Canada.

United States: Examples of non mandatory standards are those issued by ASME, ANSI, NFPA etc. That may be adopted by regulatory bodies. Current mandatory regulations are title 49 of CFR (Code of Federal Regulations) and the requirements of DOT (Department of Transport). General industrial safety materials including the production and handling of transformer oil are regulated by OSHA (Occupational Safety and Health Administration).

Federal republic of Germany: Mandatory regulations for installations and instructions for the prevention of accidents instructions for the transport of dangerous goods.

CONCLUSION

We know the present century is the century of industrialization. A careful out looking of the developed countries established the fact that no nation can step forward without rapid industrialization. Although our country is on agri-based, its economical condition is not stepped forward for the shortage of small and large industry especially for the petroleum refinery industry. Bangladesh is least development country. The industry will be able to contribute to the national economy and at the same time will provide a number of employment people.

Some important properties of transformer oil such as water contents, Pour point, flash point, viscosity and color slandered of used transformer oil, virgin transformer oil base stock obtained from crude oil and different grade of fresh transformer oil have been studied   due to comparison.

From the above description about transformer oil industry, we find that the demand of transformer oil is about 2000 Metric Ton in our country.

From the literature survey we can easily say that a lot of amount of transformer oil is used in the various capacity of transformer.  So transformer oil will be always demandable for our country and its demand will increases in Bangladesh with the increase of number of transformer.

The fuel and water supply can be easily meet up by Titas gas and rivers. Land cost in our country is very lower than that of other foreign country. The proposed industry is petroleum refinery based industry and will not handle too much explosive hazardous chemicals so the risk factors are minimum. It will also less environmental pollution related industry.

From the discussion of technology that its manufacturing process is easy. Required equipments and machines are not so complicated. Some of the equipments must be imported from foreign countries. Additives must be imported from foreign countries because these are not produced in our country. Petroleum is available in our country. Since transformer oil manufacturing process is basically a petroleum refinery product (originated from lubricating oil) there is possibility to set up a transformer oil industry in our country in future. The most advantage of manufacturing transformer oil is that there is no severe environmental pollution occurs during the process. From the economic studies we see that for making a industry which have a capacity to fulfill the demand i.e. 2000 MT/ year need a lot of capital investment.  The working capital investment per year is high which also contain the machinery and    equipment cost. Though equipment and machinery expense is high, calculation showed that we have a annual rate of return about           % for 2000 MT/year capacity which is acceptable for our country and the product can be supplied at imported rate or lower than imported rate.

The break-even point unit is    Metric Ton which is      % of annual capacity i.e. 2000 MT. If the money for capital investment is not available then we can import raw material at 3 month basis which reduce capital investment or we can produce one portion of our demand and other portion are imported which reduce capital investment

From the above works I would like to say certainly that the establishment of transformer oil base stock industry will be beneficial and profitable in the context of Bangladesh.

REFERENCES

1.            Petroleum Refinery engineering

By- W. L. Nelson.

2.            The chemistry and technology of petroleum

By- James G. speight.

3.            Transformer

By- BHEL

4.            Transformer Oil

By- R.A. Lipshtein and M. I. Shakhnovich

5.            Modern petroleum Technology

By- G.D. HOBSON.

6.            The petroleum Hand book

By- ELSEVIER

7.            Shreve’s Chemical process industries

By- GEORGE T. Austin

8.              Outlines of chemical technology

By- DRYDENS

9.            Industrial Chemistry

By- R.K. DAS

10.        Industrial Waste water treatment

By- M.N. RAO, A.K. DATTA

11.        Encyclopedia of chemical technology

By- Krick Othmer

12.        Environmental chemistry

By- Moore, John W., Elizabeth.

13.        Hand book of chemical Engineering

By- Perry

14.        Liquid- Liquid Extraction

By-L. Alders

15.        Unit operations of chemical engineering

By- McCabe, Smith.

16.        Plant design and economics for chemical engineers

By- Max. S. Peters, Kians, D. Timerhaus.

17.        Encyclopedia Americana

Vol. 22

18.        Abstract of chemical technology

Vol. 52

19.        Environmental pollution and management.

By- Pramed singh.

20.        SIRI Illustration catalogue of machines

By- O. M. Tandon

21.        The new encycloptedia Britannica

Vol. - 14

SOURCE OF INFORMATION

1.                Power development Board (PDB)

Abdul goni road, Dhaka

2.                Rural Electrical Board (REB)

Khilkhet, Dhaka.