Field of the Invention
[0001] The invention relates to methods of removal of hydrocarbon impurities such as crude
oil, petroleum products, lubricating agents, fats of technical and household grades
and oils and can be applied in different fields of industry for chemical- and mechanized
washing and cleaning of process and transportation means.
Description of the Prior Art
[0002] The process of treatment (cleaning, washing, degreasing) of equipment, mechanisms,
units and parts, as well as vessels and reservoirs contaminated with crude oil, petroleum
products, fats and other liquid hydrocarbons is one of the most urgent problems both
from the point of view of the working, environmental and fire safety and financial
expenditures.
[0003] Previously applied known treatment methods do not now meet modern requirements. The
cause of it is the complexity and the incomplete previous study of physico-chemical
processes taking place while liquid hydrocarbons removing from surfaces the results
of which are influenced by different factors, i.e. surface material, chemical composition
and properties of impurities, cleaning process parameters and conditions, composition
of technical detergents, peculiarities of detergents interaction with impurities and
so on.
[0004] Some methods and compositions as well as various solvents are known and widely used
in industry, to clean metal surfaces of oil-, mud-, crude oil- and asphalt- and pitchy
impurities. As a rule, universal solvents are used which can dissolve various substances
contained in such impurities as aceton, kerosene, whitespirit and so on (B.G. Petrik,
P.V.Choulkov and S.I. Kalashnikov "Handbook: Solvents and compositions for cleaning
machines and mechanisms", Moscow, "Khimia", 1989). Main operations included in these
methods are washing of surfaces to be treated, pumping-off of formed emulsion of solvent
and liquid hydrocarbons and its removal followed by discharging into treatment facilities.
[0005] High fire hazard and ecological harmfulness for the environment and attending personnel
are the main drawbacks of various liquid solvents used as detergents. Known solvents
of high ignition temperature (trichloroethane, trichloroethylene and others) though
reducing flammability are extremely toxic and dangerous for attending personnel's
health and therefore require very strict observance of safety measures.
[0006] The method of petroleum products removal from surfaces is known (USSR, Author's certificate
No 944685) which consists in surface cleaning with the aqueous solution of detergents
based on surfactants and electrolytes which forms stable emulsion with hydrocarbon
impurities. To clean a surface using a closed-cycle method, washing solution is regenerated
by the phase separation of emulsion with the help of the electric flotation followed
by the removal of organic phase and the return of water suspension into the cleaning
cycle.
[0007] The above-mentioned method ensures the required level of surface cleaning and the
possibility to repeatedly use washing solutions, still the technological process is
complicated owing to the formation of stable emulsion which needs either long-time
settling or the additional separation by any other method.
[0008] The method is known of hydrocarbon impurities removal from surfaces, particularly
of oil-and fat contaminants (RU, No 2019318) with the use of two liquids. Washing
of an article surface in conformity with this method is performed with washing solution,
but impurities are removed from the washing solution with the help of auxiliary liquid
which does not form stable emulsion with washing solution and additionally can selectively
recover oil-and fat contaminants from it. When the washing procedure is over the auxiliary
liquid is regenerated particularly by distillation and returned into the washing cycle.
[0009] This method has drawbacks, i.e.: using two liquids what complicates the flow sheet,
requires an additional equipment and thus increases expenditures for surface cleaning.
[0010] Methods are known of crude oil impurities removal from surfaces with the help of
coagulants and various depressing agents, i.e. additives containing hydrocarbon solvent
and polymers (RU, No 2109583) or hydrocarbon aqueous suspension and nitrogen, phosphorus
and potassium salts (RU, No 2104103) followed by washing of an internal surface with
hot water or live steam.
[0011] These methods have drawbacks, i.e. the high process temperature (up to 95-100°C)
what increases power consumption and bulkiness of the cleaning process equipment.
[0012] The method described in RU, No 2135304 is the closest to the one offered. Its essence
consists in the following: a surface contaminated with various hydrocarbon impurities
is washed with detergent aqueous solution capable of emulsifying hydrocarbon impurities.
The washing solution is then regenerated with the help of the emulsion phase separation
followed by the organic phase separation and the water phase returning to the cleaning
cycle. The "UBON" technical detergent (RU, No 2101337) or "BOK" detergent (RU, No
2132367) are used as washing solutions forming non-stable emulsions with hydrocarbon
impurities.
[0013] The above-mentioned "UBON" detergent has the following composition,
% ww: sodium salt of polyacrylic acid modified by ether groups - 0.1 - 10; electrolyte
- 0.5 - 40; water - up to 100.
[0014] The "BOK" detergent has the following composition, % ww: nonionic surfactant - 0.2
- 14; polyelectrolyte - 2.5 - 5.5; an active additive - the rest. Acrylic acid polymers
are used as polyelectrolyte in the said compound, e.g. sodium salt of carboxymethyl
cellulose (Na-CMC) and sodium carbonate or sodium carbonate combined with sodium carbamide
and / or metasilicate as an active additive. Neonol or synthanol are used as nonionic
surfactants in the said detergent composition.
[0015] To eliminate organic impurities penetrating into washing solution, the emulsion phase
separation is performed in a separation vessel and the water phase to be returned
into the washing cycle is passed through an intermediate reservoir. Water phase is
taken from the bottom part of the separation vessel and supplied to the cleaning cycle
from the bottom part of the intermediate reservoir. During the process of the emulsion
phase separation a volume ratio of organic impurities and washing solution is provided
for not less than 1 : 2.
[0016] The said method ensures the required level of surface cleaning and the possibility
to repeatedly use washing solution, still a desired result is achieved by the flow
sheet complication as separate stages of the process take place in intermediate vessels
but the provision for a volume ratio of impurities and washing solution requires the
evaluation of a volume of impurities to be removed before the beginning of a surface
cleaning process. Such an evaluation is rather difficult to be done accurately.
[0017] When using the "BOK" technical detergent as washing solution it is necessary to take
into account that neonol and synthanol belong to nonionic surfactants causing heavy
foam formation and while preparing washing solution at relatively low temperatures
they can decompose loosing their properties. Using metasilicates in washing solution
is also undesirable as they can be a cause of a tank internal surface corrosion.
[0018] Polyelectrolytes tend to form polymer-colloid complexes what can cause the reduction
of organic compound recovery and washing solution purification level.
Brief Summary of the Invention
[0019] The technical object of the supposed invention is the simplification of the technological
process of cleaning, the increase of hydrocarbon impurities recovery during the washing
solution regeneration and the reduction of power consumption for the cleaning process.
[0020] The technical object is achieved owing to the fact that some changes and modifications
have been introduced into the known closed-cycle method of hydrocarbon impurities
removal from surfaces which includes the preparation of detergent aqueous solution
containing nonionic surfactant and an active component, surface washing-off with detergent
aqueous solution, pumping-off of the obtained emulsion, separating of the emulsion
into aqueous and organic phases followed by the return of the aqueous phase into the
cleaning cycle and the periodical discharging of the organic phase to a storage tank.
[0021] The role of nonionic surfactant is played by a nonionic surfactant based on fatty
alcohol alcoxylate in quantity 2 - 4 % ww and an active component in quantity up to
100 %.
[0022] The separation of emulsion to be pumped-off into water- and organic phases is carried
out by passing it through a self-cleaning thin-layer settler (separator).
[0023] The role of fatty alcohol alcoxylate is played by oxyethylated polyoxypropylene glycol
derivatives of ethylene diamide or oxyethylated polypropylene ethylene diamine known
under trademarks "Akatronic EDP, EGE, PGP" and others possessing a number of useful
properties including emulsifying and thickening characteristics.
[0024] As an active component of a detergent, soda ash is used or a compound with a partial
soda ash replacement by phosphoric acid sodium salts, the component weight ratio being
equal to 1.9 - 2.3 : 1.
[0025] As phosphoric acid sodium salts, tripolyphosphate or trisodiumphosphate or their
mixture are used.
[0026] Depending upon an impurity type (crude oil, fats, oil) and material of a surface
to be cleaned (steel, aluminium or other non-ferrous metals) aqueous washing solution
is used with a fluctuating content of detergent, i.e. from 1.5 to 4.0 % ww; washing
solution temperature is selected within the limits of 40 - 55°C.
[0027] The whole complex of characteristics allows to achieve a number of advantages in
comparison with known technical decisions, namely:
- to increase the level of hydrocarbon compounds recovery from contaminated washing
solution up to 97 - 98.5 %;
- to reduce power consumption owing to the reduction of washing solution temperature
in the course of the cleaning process;
- to improve the environment quality and attending personnel's working conditions owing
to the elimination of harmful and hazardous components from detergent composition;
- to reduce cost and time of hydrocarbon impurities removal from an actual area unit
at the expense of the efficiency of the detergent composition offered.
Brief Description of the Several Views of the Drawings
[0028] Fig. 1 represents a flow diagram of hydrocarbon impurities removal from a surface
using the example of a railway tank cleaning.
Description of the Preferred Embodiment of the Invention
[0029] The method of hydrocarbon impurities removal from a surface includes the following
sequence of operations:
- the preparation of washing solution of a predetermined concentration on the basis
of detergent of the composition selected;
- warming and supplying washing solution for washing-off of a contaminated surface;
- pumping- off the contaminated washing solution (emulsion) into a vessel with washing
solution having preliminary passed it through a self-cleaning thin-layer settler;
- discharging an organic phase from the self-cleaning thin-layer settler to a tank containing
separated petroleum product;
- removing sludge from the self-cleaning thin-layer settler;
- if the washing solution is repeatedly used its alkalinity should be controlled and
if its concentration fluctuates from a predetermined one it is adjusted by adding
water and detergent.
[0030] The composition of a detergent to be prepared is determined proceeding from a number
of factors, i.e. impurity composition, material from which a tank or other vessel
are made, impurity age and so on.
[0031] The use of nonionic surfactant based on fatty alcohol alcoxylate as nonionic hydrophilic
surfactant is substantiated with the fact that it is well dissolved in water and distinguished
with low foam formation in neutral and alkaline media. Besides, it possesses high
surface- and interphase activity in an alkaline medium and good wetting properties
on a polar and a hard surface and has emulsifying and thickening characteristics as
well.
[0032] The selection of such a quantitative composition is explained with the fact that
if nonionic surfactant content is less than 2.0 % ww the cleaning process indices
are reduced as hydrocarbon impurities detachment from a surface to be cleaned becomes
difficult and the cleaning rate becomes slower; if nonionic surfactant content is
more than 4.0 % ww financial expenditures for cleaning are increased what is inexpedient
as cleaning process cost grows.
[0033] Soda ash is most often used as an active component as it is the cheapest and widespread
detergent though its efficiency is somewhat less than the efficiency of more expensive
detergents, e.g. tripolyphosphate and trisodiumphosphate. Still, in those cases when
hydrocarbon impurities, especially inveterate ones have very complex composition or
a surface is very contaminated, a more efficient detergent is worth while to be used.
Such a necessity may arise if soda ash or time are deficient and sodium salts of phosphoric
acid being available.
[0034] The experience has shown that to achieve optimum indices of cleaning it is enough
to replace approximately 30 % soda ash, i.e. the ratio "soda ash : sodium salt of
phosphoric acid" should be within the limits of 1.9 - 2.3 : 1. If the ratio is more
the cleaning quality may not be achieved; if the ratio is less the cleaning process
cost price grows.
[0035] The range of the admissible concentration of washing solution equal to 1.5 - 4.0
% ww is selected on the basis of the study carried out with the use of washing solutions
obtained from the said compositions to remove liquid hydrocarbons from surfaces. It
was found that if a tank is made of non-ferrous metal e.g. aluminium it is better
to use detergent aqueous solution of 1.5 - 2.5 % concentration, but if a surface is
made of steel or cast iron it is better to use detergent aqueous solution of 2.0 -
4 % concentration.
[0036] If the concentration of washing solution is smaller time of the cleaning process
increases, if the concentration is higher cleaning expenditures increase.
[0037] After a predetermined composition of detergent has been selected and diluted to a
predetermined concentration (the preparation of washing solution can be carried out
in a separate vessel or directly in vessel 3) pressure pump 4 conveys it through heat
exchanger 5 to washing heads 2 installed in tank 1. Washing solution warming up to
40 - 55°C is performed in heat exchanger 5. Concrete temperature is selected proceeding
from the detergent composition, solution concentration and optimum cleaning time.
At temperatures lower than 40°C the cleaning process time is significantly increased
but at temperature higher than 55°C the cleaning process efficiency is reduced as
foam formation increases what makes difficult the process equipment operation; nonionic
surfactant activity drops. Owing to washing heads of a turbine type an internal surface
of a vessel to be cleaned is washed by the spray washing method. To achieve maximum
efficiency, washing heads are arranged so that their orientation could be changed
if necessary. Average washing time is 8 - 20 minutes.
[0038] Spent washing solution is with the help of diaphragm pump 6 supplied to the self-cleaning
thin-layer settler 7 where liquid phase is separated into washing solution which,
while being cleaned, is fed to vessel 3 for the subsequent use, and into lighter phase,
i.e. hydrocarbon impurities which are accumulated in the upper zone of separator 7
and as far as they are accumulated they are pumped into storage vessel 8 for decanted
product; sludge is accumulated in the lower, stagnant zone of the separator.
[0039] The self-cleaning thin-layer settler is a coalescing separator in the casing of which
a plane-parallel packing is installed. Self-cleaning of the packing is achieved by
the selection of the treatment modes, as well as of appropriate slope of plates which
depends upon the composition and properties of the mixture to be separated. A slot
gap between plates is provided owing to packings. A mixture to be separated (emulsion)
is supplied into the gap through an upper branch pipe and distributed among slot channels
which have three areas, i.e. a vertical area where the separation of petroleum product
particles takes place at the plate walls; a rotary area where the flow changes its
orientation in the gravitational field and an expanding area where the separated organic
phase floats up to the upper part of the apparatus and is discharged into the decanted
petroleum product tank. Settled sludge is removed through the bottom branch pipe of
the self-cleaning thin-layer settler.
[0040] In comparison with the best foreign analogues, e.g. the analogue developed by the
company Utility Vault Co, the self-cleaning thin-layer settler does not require frequent
stops and dismantling to clean and regenerate the plane-parallel packing. In comparison
with settlers equipped with a crimped packing "Quantek" with 45° slope the above-mentioned
settler ensures any slope of plates and does not require repeated agitating of separated
phases.
[0041] In the course of the repeated use of washing solution its concentration is controlled
according to an alkalinity value with the help of hydrochloric acid titration using
methyl orange indicator and if necessary it is adjusted by adding water and detergent
into vessel 3. The dependence of washing solution total alkalinity upon its concentration
is shown in Table 1.
Table 1
Washing solution concentration, % ww |
Solution density at 20°C, g/cm3 |
Total alkalinity of washing solution, % |
1.5 |
1.012 |
1.3 |
2.0 |
1.018 |
1.6 |
2.5 |
1.024 |
2.0 |
3.0 |
1.029 |
2.6 |
3.5 |
1.034 |
3.1 |
4.0 |
1.0385 |
3.7 |
[0042] Usually the solution adjustment is carried out in 6 - 8 cycles of the cleaning process
by adding freshly-prepared washing solution in a quantity sufficient to bring the
total concentration of the solution to a predetermined value.
[0043] In conformity with the flow sheet shown in Fig. 1 it is possible to wash railway
tanks and tank trucks, vertical, horizontal and underground stationary reservoirs,
as well as other vessels for storage and transportation of liquid hydrocarbons. Concrete
examples of the method implementation are given below.
[0044] Example 1: Washing of a steel tank, 63 m
3, was performed with 3.5 % solu-tion of detergent (35 kg of detergent per 1000 liter
of water) of the following com-position: 3.0 % ww nonionic surfactant representing
oxyethylated polyoxypro-pylene glycol derivative of ethyldiamine (Alcatronic EDP)
and 97 % ww soda ash.
[0045] The said washing solution was from reservoir 3 (Fig. 1) taken for washing from the
reservoir bottom flange with the help of ejector pump 4 and supplied to washing heads
2 installed inside the tank, each of the heads having two nozzles. Pressure of washing
liquid was 1.5 MPa. Washing solution temperature was controlled with the help of a
thermometer and maintained within the range of 45 - 55°C owing to its warming by heater
5. After 10 minutes of spray washing the obtained emulsion representing the mixture
of washing solution and liquid hydrocarbons was pumped off with the help of diaphragm
pump 6. Contaminated washing solution was supplied to the upper part (a branch pipe)
of the self-cleaning thin-layer settler 7. The passage of emulsion representing the
mixture of washing solution and liquid hydrocarbons through the self-cleaning thin-layer
settler allowed to remove the basic volume of impurities at this stage and thus to
practically eliminate the stage of the gravitational settling of contaminated washing
solution. Cleaned washing solution was directed via the upper branch pipe to the reservoir
3 containing washing solution. Time of phase separation was only several minutes.
[0046] Organic phase floated up into the upper part of the settler 7 and was removed with
the help of a pump or special fat catchers into the storage tank of decanted product
8. Such a separation of emulsion resulted in 98.5 % recovery of liquid hyd-rocarbons
in comparison with 95 % for the prototype.
[0047] Periodically samples were taken through the sampler installed at the line of washing
solution supply (not shown in Fig. 1) and total alkalinity of the solution was checked.
[0048] In Example 1 approximately 30 liter of water and 800g of detergent were added after
eight washing cycles for the adjustment of the concentration predetermined.
[0049] Example 2 : Washing of the similar railway tank was performed, but detergent composition
was changed by the partial replacement of soda ash with sodium salt of phosphoric
acid. The detergent had the following composition, % ww: nonionic surfactant - 3.0;
tripolyphosphate - 30 and soda ash - the rest to 100. Washing solu-tion concentration
was 3.5 % as in Example 1. The washing process was carried out similar to one described
in Example 1, but time of the tank washing reduced to 7.5 minutes.
[0050] The level of hydrocarbons recovery from emulsion was 98 %.
[0051] Example 3: Cleaning of a brass reservoir, 5 m
3, of machine oil drain residues was performed. 20 kg of detergent having composition
corresponding to Example 1 were dissolved in 1000 liter of water at 45°C while permanently
agitating. The reser-voir cleaning was performed similarly to one described in Example
1.
[0052] Washing time was 6 minutes, the level of hydrocarbons recovery was 97.5 %.
[0053] Example 4: Cleaning of a reservoir similar to one represented in Example 3 was performed
but the detergent had the following composition, % ww: nonionic surfac-tant based
on oxyethylated polypropylene ethylene diamine as fatty alcohol alcoxy-late - 3.0;
trisodiumphosphate - 20.0; tripolyphosphate - 12.0 and the rest was soda ash - to
100. Concentration of the said detergent aqueous solution was 2 % as in Example 3.
[0054] Washing time was 5 minutes, the level of hydrocarbons recovery (machine oil) was
98.5 %.
[0055] The method was approbated with respect not only to railway tanks, but to ot-her articles.
Thus, Table 2 gives data concerning cleaning reservoirs for petroleum product storage
and Table 3 gives data concerning cleaning vertical cylindrical reservoirs of different
volumes installed under a panel roof. Washing solutions containing 3 - 4 % of detergents
were used. different volumes installed under a panel roof. Washing solutions containing
3 - 4 % of detergents were used.
Table 2
Reservoir |
Internal diameter, m |
Length, m |
Actual volume, m3 |
Internal surface area, m2 |
Losses of technical detergent, kg |
Mean time of washing off, min |
PS-25 |
2.0 |
8.3 |
20.8 |
58.4 |
0.3 |
6 |
PS-50 |
2.4 |
11.3 |
41.5 |
94.9 |
0.5 |
10 |
PS-100 |
3.0 |
14.6 |
82.6 |
140.7 |
0.7 |
14 |
PS-160 |
3.4 |
18.5 |
133.0 |
200.4 |
1.0 |
20 |
PS-200 |
3.4 |
22.9 |
166.0 |
262.7 |
1.3 |
26 |
BS-50 |
2.4 |
11.5 |
41.0 |
96.4 |
0.5 |
10 |
BS-100 |
3.0 |
14.6 |
82.6 |
151.6 |
0.8 |
15 |
BS-160 |
3.4 |
18.2 |
133.0 |
198.3 |
1.0 |
20 |
BS-200 |
3.4 |
22.6 |
166.0 |
259.5 |
1.3 |
26 |
Table 3
Reservoir |
Internal diameter, m |
Height, m |
Actual volume, m3 |
Internal surface area, m2 |
Losses of technical detergent, kg |
Mean time of washing off, min |
PBC-200 |
6.6 |
5.9 |
204 |
177.7 |
0.9 |
18 |
PBC-300 |
7.5 |
7.3 |
332 |
264.7 |
1.3 |
25 |
PBC-400 |
8.5 |
7.3 |
421 |
313.7 |
1.6 |
30 |
PBC-700 |
10.4 |
8.8 |
757 |
457.0 |
2.3 |
45 |
PBC-1000 |
12.3 |
8.8 |
1056 |
581.0 |
2.9 |
60 |
PBC-2000 |
15.2 |
11.8 |
2135 |
924.9 |
4.6 |
90 |
[0056] On the average, when using a detergent containing the similar quantity of nonionic
surfactant and different active components (only soda ash or its partial replacement
with sodium salts of phosphoric acid) time of washing differs by 8-12 %. To keep time
of washing unchanged, the washing solution concentration should be reduced by 0.10-0.18
% ww. Hydrocarbon recovery is 97.5-98.5 %.
[0057] It is possible to make a conclusion that the efficiency of the use of self-cleaning
thin-layer settlers is increased owing to the fact that an electrostatic charge of
contaminated solution does not arise as a result of the use of washing solution of
the said composition. It is practically neutral, therefore the organic phase is pressed
to plates and spread all over their surfaces increasing the level of separation from
the contaminated solution.
[0058] Thus, in comparison with known methods of hydrocarbon removal from surfaces and compositions
of a detergent being used for these purposes the proposed method has several advantages,
namely:
- the increase of hydrocarbons recovery from contaminated washing solution up to 97
- 98.5 %;
- the reduction of power consumption owing to the washing solution temperature reduction
in the course of the cleaning process;
- the elimination of the use of more expensive detergents which additionally contain
sodium salts of polyacrylic acid and corrosion inhibitor;
- the improvement of the environment and of attending personnel working conditions owing
to the elimination of the above-mentioned components;
- the reduction of cost and time of hydrocarbon impurities removal from a unit of an
actual area.
Industrial Applicability
[0059] The method may be used in various branches of industry particularly in shipbuilding,
transport, petroleum producing- and refining industry where the necessity exists to
wash storage vessels and transport liquid hydrocarbons.