WO2019197690A1

WO2019197690A1 - Method for extracting viscous hydrocarbons from storage tanks and from process equipment

Info

Publication number: WO2019197690A1
Application number: PCT/ES2019/000031
Authority: WO
Inventors: Evaristo Fontecha Cuetos
Original assignee: Evaristo Fontecha Cuetos
Priority date: 2018-04-12
Filing date: 2019-04-09
Publication date: 2019-10-17
Also published as: ES2727155A1

Abstract

The invention relates to a method characterised by injecting into the tank or equipment a stream of gases homogenised by means of an irreversible turbulent diffusion process, the stream being made up of recirculated gases from the same tank or equipment, steam and inert gas. Homogenising steam with the other gases prevents the free rising movement thereof, thus managing to transfer large amounts of latent heat to the hydrocarbons (539.4 cal/g at 100ºC) by condensing thereon a much greater percentage of the injected steam. The heat transferred to the hydrocarbons makes them flow towards the suction side of the pump, while the inert gas and the recirculation prevent the risks of fire and polluting emissions. Floating-roof oil tanks and equipment provided with demisters are two representative uses of the method.

Description

I PROCESSED OE EXTRACTION OF VISCOSE TANK HYDROCARBONS OE STORAGE AND PE PROCESS EQUIPMENT

OBJECT HEARS THE INVENTION

to

Storage tanks and process equipment should be emptied regularly to perform regulatory inspections, maintenance work, cargo changes or demolition. The object of the present invention is a method of extracting viscous hydrocarbons from 0 storage tanks and gives equipment of a process characterized by including an operation with which it is possible to inject into the tank or equipment a homogenized gas stream by means of an irreversible process of turbulent diffusion, the current being constituted by gases in retreatment of the tank or equipment itself, water vapor and inert gas.

5 The procedure is applicable to storage tanks and hydrocarbon process equipment existing in oil fields, “fracking ^* farms. petroleum refineries, petrochemical plants, port terminals, etc. As representative applications of the procedure, it is worth mentioning the oil floating roof tanks and the Q process equipments provided with “demistors” fdesnebulizers) of gaseous hydrocarbons,

STATE OF THE TECHNIQUE 5 The process object of the invention has as background three procedures for the selective extraction of viscous hydrocarbons from storage tanks that were the object of a patent application by the same inventor as the present procedure, with the dates and application numbers indicated below: 04.28.201 1 / P201 100484; 0 24.01 .2014 / P2G140GQ80; and 07.01 .2010 / P201800Q07.

The procedures of the first two inventions establish the injection of hot air into the tank, but not the injection of water vapor which does establish the procedure of the third invention. The heating capacity of water vapor is much higher than that of hot air, so the process of the third invention is much more effective for heating and extracting hydrocarbons than its two antecedents, although with the inconvenience of forcing treatment of the hydrocarbons extracted to eliminate the condensates generated by water vapor. The process of the present invention also has the disadvantage that water vapor generates condensates, but is more effective than that of the third invention, since in order to obtain the same results, it requires a lower amount of water vapor and electrical energy . The homogenization of the gas stream prevents the free upward movement of the injected water vapor, thereby reducing the percentage of water vapor that condenses inefficiently on the roof of the tank or equipment and increasing that condensed on the hydrocarbons , giving them directly 15 large amounts of latent heat (539.4 cal / g to 100 ^a C). In addition, to recirculate the gases, large energy losses are avoided by the emission into the atmosphere of a large amount of hot gases and water vapor.

When the third preceding procedure is used, the oxygen concentration inside the tank remains close to 21%, except in 20 areas close to the injection of water vapor, so there are risks of fire and explosion when exceeded in the inside the tank the flash temperature of the hydrocarbons. On the other hand, with the process of the present invention, the flash temperature of the hydrocarbons can be exceeded in completely safe conditions, since inert gas is injected into the tank or equipment to maintain the oxygen concentration in values that ensure a range of null flammability.

The elimination of pollutant emissions using the background procedures would entail unassuming costs of gas purification, while with the process of the present invention the recirculation

30 tion of gases from the tank or equipment itself avoids the greatest part of the emissions of pollutant gases into the atmosphere and also makes it possible to eliminate almost all of the emissions at an assumed cost. For the above, e! The procedure object of this invention is more effective, safe and environmentally friendly than the three previous procedures,

As of the date of presentation of the present invention, the procedures most commonly used in refineries to extract viscous hydrocarbons remaining in oil tanks are based on dilution with light crude oil supplied by the refineries themselves. The process object of the invention has important advantages over the dilution processes mentioned, such as not requiring the supply of light crude to dilute the remaining hydrocarbons, extracting coughs without mixing them with the contaminants deposited in the bottom of the tanks, avoiding dangerous Leaks and extensive contamination of soils inherent to dilution operations with light crude in tanks with non-watertight funds, and make use of simple and easy-to-install extraction equipment that greatly reduces execution costs. As far as the process equipment is concerned, the most widespread procedures are based on cleaning with pressurized water and chemical cleaning, compared to which the present procedure has the advantages of having lower running costs and of generate less waste

DESCRIPTION OF THE INVENTION

The process of extracting hydrocarbons from storage tanks and process equipment object of the present invention is based on subjecting an irreversible process of turbulent diffusion a stream consisting of gases in recirculation of the tank or equipment itself and by the amounts of steam from water and inert gas that are required at all times to heat and extract hydrocarbons in an effective, safe and environmentally friendly way.

Cash. The turbulent diffusion forces a rapid and irreversible ho-genizadón of the gas stream that prevents the free upward movement of water vapor in the tank or equipment, despite its lower density Give, and recirculation, establish homogenous water vapor flows with the gas gases between conveniently chosen tank points or equipment. If the water vapor is not homogenized with the other gases, most of it will be inefficiently condensed on the roof of the tank or equipment while with the homogenized it is possible to yield large amounts of latent heat to the hydrocarbons {539.4 cal / ga 100 ^ft C) when a much higher percentage of water vapor condenses on them. The homogenous gas stream in turn generates diffusive flows of water vapor and inert gas in the rest of the tank or equipment. In stationary states, the first law of Fck relates the diffusive flow with the gradient of the concentration of the gases and Flck's second law predicts changes in gas concentration over time. The diffusive flow of inert gas in jected are effective to maintain the oxygen concentration in all areas in tanks or equipment in values that ensure range ^¬ flammability null, pear diffusive flow of water vapor are less effective than that the laws of Fíck establish due to the decreases in the percentage of water vapor that are experiencing the gas flows inside the tank or equipment with the condensations. For this reason, several positions of the equipment with which the hydrocarbon extraction is carried out may be necessary in large tanks, so that the water vapor of the homogenous stream covers all the sectors of the tank bottom.

Insurance. The procedure establishes operations that eliminate the risks of fire and explosion through the initial contribution of inert gas, until reaching an oxygen concentration that ensures a zero flammability range, and subsequent contributions of inert gas to the turbulent diffusion device to counteract the increases in oxygen concentration due to the entry of air into the tank or equipment during the application of the procedure. On the other hand, the contribution of the inert gas that would be needed would be economically unviable if a volume of gauze equivalent to that of the injected gases were released directly into the atmosphere. The water vapor of the homogenous stream also contributed. flees to reduce the concentration of oxygen in the tank or equipment.

Environmentally friendly. The redrculation of gas coughs by itself avoids most of the pollutant emissions or the unacceptable costs that would mean purifying gas flows equivalent to those injected into the tank or equipment. The procedure also makes it possible to eliminate virtually all of the pollutant emissions at an assumed cost, sealing the tank or equipment and leaving a vent line to which a gas purification unit is connected. In this way, polluting emissions can be avoided in the initial operation of Inert gas injection, in the final operation of ventilation of the tank or equipment, in the increases in volume that the gases experience when the temperature inside the tank or equipment rises and at times in which the amount of gases injected into the tank or equipment is greater than that of the recirculating gases and the water vapor that condenses.

The method of extracting viscous hydrocarbons from storage tanks and process equipment comprises the following sequence of operations:

Previous operations: installation of the equipment necessary to carry out the extraction of hydrocarbons, grounding of all extraction equipment that maintains contact with hydrocarbons; sealing of the tank or process equipment maintaining a vent line, and injection of inert gas into the tank or equipment until an oxygen concentration is achieved that ensures a zero flammability range, which implies in hydrocarbons with low flash temperatures to have that reach percentages of oxygen lower than 8%. The vent line can be connected to a gas purification unit, which requires it from a small centrifugal fan to drive the gases to the purification unit if the sealing of the tank or equipment is not possible.

- Inject into the tank or equipment a homogenized gas source through an irreversible process of turbulent diffusion, the current being constituted by gases in recirculation of the tank or equipment itself and by the amounts of water vapor and inert gas that are required in ca- gives time to maintain the oxygen concentration in «alores que

that flow ios hydro-

its use in potentially explosive atmospheres The flow of recirculating gases must be regulated so that a speed of passage is achieved through the detectors of the turbulent diffusion device that ensures the generation of the gas stream. The amount of water vapor that must be added to the gas stream is regulated so that the heat transfer to the hydrocarbons causes them to flow in an amount equivalent to that demanded by the pump. Inert gas counteracts the increase in oxygen concentration by air entering the tank or equipment, adding to the gas stream in the amount determined by measurements either in the tank or equipment or in the external gas circuit in recirculation. In the case of high-temperature hydrocarbons such as asphalts, inert gas does not need to be added. To recirculate the gases and force their turbulent flow through the diffusion device, one or more centrifugal fans suitable for use in potentially explosive atmospheres (ATEX centrifugal fans) are used. ATEX blowers with the advantages over centrifugal fans can be used to increase the speed of passage of gases through the detectors of the turbulent diffusion device and to produce a heating of the gases in recirculation of the tank or equipment without compression. reach at any time the self-ignition temperature of hydrocarbons. The turbulent diffusion device is provided with detectors or similar components that promote turbulent flows and a purge line to extract the condensates that are formed in the assignments of latent heat of the water vapor to the device itself and to the gases that pass through it. The temperature of the water vapor, which does not reach the self-ignition temperature of the hydrocarbons at any time, is generally between 120 and 200 ^H G. The heating of the recirculation gas stream and the inert gas is carried out by means of the heat transfers from water vapor in the turbulent diffusion device, heat sensitive and mainly latent heat when condensed A turbulent diffusion device can be used, provided with its own system of heating the gases that pass through it to prevent the temperature of the water going down to values that negatively affect the effectiveness of the process. The heating system of! turbulent diffusion device, which does not reach at any time the temperature of self-ignition of hydrocarbons, may be constituted by ATEX electrical resistors or by a heat exchanger through which a thermal fluid circulates The points between which the gases are recirculated They must be located in the lower areas of the tanks or equipment. The man nozzles of the tanks or equipment can be used as recirculation points by installing covers with fittings for the connection of suction and gas supply hoses. In medium-sized tanks and in process equipment, a single positioning of the equipment necessary to carry out the extraction of hydrocarbons, preferably between two man mouths or diametrically opposite points, is sufficient. In tanks of small size and in process equipment, the gas redrculation can be established between two points located in the same manhole but orienting the suction and discharge hoses of the gases in recirculation so that the flow is favored steam gives water from the bottom of the tank or equipment. In large tanks, up to four positions may be necessary, preferably between manholes located at 90 ^a , so that with each positioning the water vapor of the hydrogen flow and its diffusive flows circulate through a sector that is equally a quarter of the bottom surface of the tank.

- Extract the hydrocarbons by means of a pump suitable for use in potentially explosive atmospheres, and additional heating of the hydrocarbons can be carried out to facilitate extraction and subsequent transfers. Additional heating can be carried out by means of heating devices located inside the tank or equipment and in the vicinity of the suction line of the pump (ATEX electrical resistors, steam coils, etc.) or by means of a heating band of the lower outer strip of the tank or equipment. The heating band must be placed close to the pump suction line and can be heated electrically or by circulating hot air and water vapor between the band itself and the metal surface strip of the tank or equipment covered by the band Heating devices In addition, the autoignition temperature of hydrocarbons is not reached at any time. The hydrocarbons are transferred to the designated point for treatment, tank transport or storage in an adjoining tank. Once the heat input ceases to be effective and the flow of hydrocarbons to the suction lines ends, the extraction is terminated. The interior of the tank or equipment will be inspected and, if significant amounts of hydrocarbons remain in any area of the tank or equipment, the extraction will continue by choosing the gas recirculation points of the tank or equipment so that the water vapor from the stream homogenized through the area where the hydrocarbons are located At the end of the extraction of hydrocarbons, water, oily sediments or hydrocarbons with high melting temperature remain at the bottom of the tank or equipment, which must be removed by conventional methods .

Figure 1 shows a scheme of the procedure applied to an oil tank that has a floating roof -1- and several manholes in which the covers with connection fittings -2- are installed. A centrifugal fan -3- and a blower -4- used in potentially explosive atmospheres force the recirculation and turbulent flow of gases from the tank by a turbulent diffusion device -5- provided with detectors -8- and a condensate drain line -7, in which the gas recirculation of the tank is homogenized with the water vapor and nitrogen provided respectively by the steam boiler -8- and the nitrogen generator -9-, while the purification unit of gases -10- avoid polluting emissions. Hydrocarbons are extracted by means of a pump -1 1- be used in potentially explosive atmospheres, which is protected by a filter -12-, while the heating device -13-, which is located next to the suction line of the pump, facilitates removal and Transfer of hydrocarbons to point -14- for treatment, transport or storage.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

An example of a preferred application of the process is in the extraction of the viscous and flammable hydrocarbons accumulated at the bottom of the oil floating roof tanks, a very advantageous application because the floating roof is positioned at the bottom of the tank on its support legs ( approximately 2 meters high) and thus the volume of the tank is greatly reduced.

The sequence of operations of the procedure is as follows:

- Previous operations: installation of the necessary equipment to carry out oil extraction; grounding of the extraction equipment that is in contact with the oil or its gases; tank sealing maintaining a vent line; and Injection of nitrogen into the tank until an oxygen concentration of less than 8% is achieved. The vent line can be connected to a gas purification unit to eliminate virtually all of the polluting emissions.

- Injection into the tank of a homogenized gas stream through an irreversible process of turbulent diffusion, the current being constituted by gases in recirculation of the tank itself and by the amounts of water vapor and nitrogen that are required at all times to maintain ia oxygen concentration below 8% and to make the oil flow in an amount equivalent to that demanded by an ATEX pump. Previously, two caps with fittings to which two ATEX centrifugal fans and a turbulent diffusion device equipped with detectors and a condensate drain line are installed in two diametrically opposed man mouths are installed. The cauda! Gauze recirculated so that a rate of passage by the detector device that ensures turbulent diffusion homogen i _l ation of the gas stream is reached. The amount of water vapor that must be added to the gauze stream is regulated so that heat transfer to oil causes it to flow in an amount equivalent to that demanded by the pump. In addition to yielding heat, the water vapor once condensed in the tank causes the oil that can be retained between sediment accumulations or in the deformations of the bottom of the tank to float and flow due to density differences. The amount of nitrogen contributed to keep the oxygen concentration in the tank below 8% is determined by making measurements in the tank or in the external recirculation gas circuit of the tank.

- Oil extraction by means of an ATEX pump, with additional heaters that facilitate the extraction of subsequent transfers. Additional heating of the viscous oil can be carried out by installing heating devices located inside the tank in the vicinity of the suction line of the pump or by means of a heating band placed on the lower outer strip of the tank, also close to the line Suction pump. The oil transfer is done to! designated point for treatment, transportation in tanks or storage in an adjoining tank Once the heat input ceases to be effective and the oil flow ends at the suction lines, the extraction is terminated. The inside of the tank will be inspected and, if significant quantities of oil remain in any area of the tank, the extraction will continue by choosing the manholes or the points between which the gases are reciruted so that the water vapor from the stream Ho ogenized through the area where oil is. At the end of the oil extraction, water, oily sediments and sometimes solid paraffins or aromatic and naphthalic compounds with high melting temperature remain at the bottom of the tank, which must be removed by conventional methods.

Claims

REIVIND CACIO IS

1. ”Procedure for extracting viscous hydrocarbons from storage tanks and process equipment, which includes the following operations:

- injecting an inert gas into the tank or equipment until an oxygen concentration is achieved that ensures a zero flammability range;

- inject in! tank or equipment a homogenized gas stream through an irreversible process of turbulent diffusion, the current being constituted by gases in recirculation of the tank or equipment itself and by the amounts of water vapor and inert gas required at any given time to maintain the concentration of oxygen in values that ensure a range of zero flammability and to make hydrocarbons flow in an amount equivalent to that demanded by a pump suitable for use in potentially explosive atmospheres; Y

- extract the hydrocarbons by means of the pump and transfer them to a designated point for treatment, transport or storage.

2. Method for extracting viscous hydrocarbons from storage tanks and process equipment according to claim 1, comprising additional heating of the hydrocarbons by means of devices located in the vicinity of a pump suction line that at no time they reach the temperature of self-ignition of the hydrocarbons.

3. ~ Procedure for extracting viscous hydrocarbons from storage tanks and process equipment according to claims 1 or 2, which also includes the use of a gas purification unit connected to the tank or equipment to eliminate contaminating emissions to the atmosphere.

4. Method for extracting viscous hydrocarbons from storage tanks and process equipment according to any one of claims 1 to 3, wherein turbulent diffusion is carried out using a device provided with deflectcres and a purge line. 5, - Procedure for extracting viscous hydrocarbons from such storage tanks and process equipment according to any one of claims 1 to 4, wherein a blower suitable for use in potentially explosive atmospheres that produces compression under heating is used of the gases in recirculation of the tank or equipment, without ever reaching the self-ignition temperature of the hydrocarbons.

8, - Procedure for extracting viscous hydrocarbons from such storage tanks and process equipment according to any one of the preceding claims, wherein the turbulent diffusion is carried out using a device provided with its own heating system that at no time reaches the autoignition temperature of hydrocarbons.