Vapour Absorb Ti On Sys

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Gasoline vapor recovery membrane system

Industry background

Petroleum consumption in China is higher than before and is more depending on

importation day by day with the speedy economic development and the more vehicle

possessions. According to statistics, the total quantity of internal petroleum and import

petroleum was about 290 million tons in 2004, including 120 million tons by import.

However, there are few concerns about the gasoline vapor volatilization in transportation

and storage. According to the detect data from gas station (without gasoline vapor recovery

system) by CARB(California Air Resources Board), there is 0.84 pound (0.38kg) wastage

from oilcan by breath when selling 1000 gallon (2952kg) gasoline, and another 8.4 pound

(3.8kg) wastage by volatilization in gasoline supplement . The gasoline vapor withdrawal

is big in the tank area: there will be 0.21% volatilization wastage by 1 temperature

increment, and more gas-phase gasoline in oilcan with the prolonged storage time. Suppose

there is 2 million tons gasoline storage in the oilcan with 50% of utility ratio by 300 days,

and the average temperature change everyday is 10 , the volatilization wastage will be

550,000 cubic meters (660 tons). The domestic data indicates, the consumption of gasoline

in all country was 50 million tons in 2003, there was at least 280 million cubic meters

gasoline wastage (340,000 tons) in transportationtransfer and distribution, and the

economic loss reached 1.3 billion RMB. According to incomplete statistics, the economic

loss by gasoline volatilization reached as high as 2 billion RMB in 2004.


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It brings plenty of saturated gasoline vapors by volatilization, which is easy to explode just

by spark or static electricity, causes hidden trouble of safety to tank area and gas station.

The greaser with vapor capture system has been installed now in some gas station in

downtown area, it has solved the volatilization during the process of oil injection, but the

vapor captured has not been reclaimed, and most vented again through breath valve, so it

has not cleared up the safety danger radically.

The gasoline vapor consists of benzene, dimethylbenzene, ethyl benzene and other

hydrocarbon mostly, carcinogenic. And most gas stations are close to the resident area, the

height of venting point is also not beyond peoples breathing space. So, we can not ignore

the dangers. The gasoline vapor will react with other nocuousness gas after irradiation by

ultraviolet radiation in air, and becomes more toxic contamination, brings more threatens to

peoples health.

In Europe and America, it began to recover gasoline vapor in 1970s, and now there are

comparatively mature gasoline vapor recovery technology and consummate laws.

U.S. Environmental Protection Agency emended Air Protection Law in 1990, it prescribed

that gas station must be installed gasoline vapor recovery equipment if its air condition can

not meet the laws. In 2001 CARB developed more strict Enhanced Vapor Recovery law,

and it declared that more advanced equipment need be installed since 2002. From 2004 to

2006, all gas stations shall be forced to install the equipment. In China, the legislation

preparation on gasoline vapor recovery is beginning. General Administration of Quality

Supervision P.R.China and Ministry of Construction P.R.China established Design and

Construction Criterion of Gas Station in 2002. It prescribed the installation of gasoline

vapor recovery and leakage checking equipment clearly.


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Gasoline vapor recovery technology

There are four kinds of gasoline vapor recovery technology by theory at present, including

absorption, condensation, adsorbtion and membrane separation.

Absorption

At normal pressure and temperature or at normal pressure and low temperature, using the

absorption liquid, such as gasoline (or waste oil), coal oil series solvent, light diesel oil,

special organic solvent, the gasoline vapor is dissolved and absorbed in the absorption

column with contacting spraying. The effect of this process is mostly depending on the

solvent, and the recovery of the solvent is generally less than 80%, there are other

disadvantages, such as more occupying room and unavailability to batch operation.

Adsorbtion

Using active carbon to adsorb gasoline vapor, the equipment consists of PSA unit,

separator and absorption column. Gasoline vapor gathered by the equipment first comes

into PSA unit where adsorption and desorption happen, the desorption gas goes through

separator and is absorbed by solvent in the absorption column. It has higher gasoline vapor

recovery, but needs more occupying room and the adsorption tower needs frequent

adsorption-desorption automatic recycling switching, and service time of active carbon is

short, so it is difficult for operation and maintenance. Otherwise, it is difficult to deal with

the waste active carbon and secondary pollution happens easily.

Condensation


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Gasoline vapor is condensed in heat exchanger with refrigerant and gasoline is recovered

directly. The temperature of the vapor is decreased to 4 in precooler and a majority of

water vapor of gasoline vapor is condensed into water and discharged. Then the

temperature of gasoline vapor is decreased to40 in the first-stage cooler, and then is

decreased to below70 in the second-stage cooler. After two stages of coolers, the

majority of VOC is recovered in liquid and gasoline vapor in discharge comes up to the

standard of 35m/l. But because of indirect heat exchange, the temperature of refrigerant

must be very low (8070 ) to guarantee higher recovery. If gasoline vapor in

discharge is required to be lower, further refrigeration is required. For condensation, safety

and gasoline vapor recovery is high, but installation cost is also great. In addition, gasoline

vapor is decreased to80~70 with refrigeration, both energy consumption and

operation costs are great.

Membrane separation

This process actually is one combination of compression, condensation and membrane, and

has grown up rapidly as modern chemical separation technology after 1960s. As the

molecular of hydrocarbon and air in the mixture are different in size, there are great

differences in permeability through the thin membrane. Based on the differences,

hydrocarbon vapor is separated from air. After mixture is compressed and condensed,

gasoline vapor is separated from air by membrane. The gasoline vapor is recirculated into

the compressor and purified air is discharged into the atmosphere. The gasoline vapor

recovery based the membrane can reach above 99%.

Gasoline vapor recovery membrane systems have many advantages including small floor


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area, simple operation, easy maintenance, safe running and high rate of return on

investment so the systems are widely applied after the systems become commercial. Since

1989, more than one hundred sets of the systems have worked in Europe. The market share

of membrane systems among newly-built gasoline vapor recovery systems reaches above

80%. In 2002 the two sets of membrane system were firstly built in America. Because of

their excellent performance, 120 sets of the membrane systems were built in 2003. Now

their market share grows up rapidly.

SDEEC's gasoline vapor recovery membrane technology

SDEEC imports world leading gasoline vapor recovery membrane technology from MTR.

The organic vapor membrane of MTR of USA is the world leader, and mainly applied in

petrochemical organic vapors recovery and nature gas conditioning. MTR is also

successful in gasoline vapor recovery, and has acquired seven patents and good

achievement in gasoline vapor recovery of big oil tank. CARBs EVR regulation of CA,

USA demands that gasoline vapor discharge standard of all gas stations in CA is improved,

and MTRs newly-developed VaporsaverTM can reach new discharge standard.

As for organic vapor membrane of MTR, please refer to Introduction to MTRs VapSep

System.

Gasoline vapor mainly contains C5~C9, and can be separated from the air based on MTRs

membrane system. The compressed mixture can be divided into permeate vapor (rich in

gasoline) and residual (purified air). The permeate vapor can be reused and the purified air

can be discharged into atmosphere directly.

Membrane Vapor Recovery Units(VRU) For Gasoline Stations


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Gasoline stations rely on vacuum-assisted dispensing systems to minimize the release of

hydrocarbon vapors to the atmosphere. These systems use a small pump to draw air and

vapors from the gasoline dispensing nozzle. For every liter of gasoline dispensed from the

pump, as much as two liters of air and gasoline vapor are returned to the storage tank.

Build-up of air in the tank leads to atmospheric releases.

MTR and OPW Fueling Components have developed a membrane vapor recovery system

for the fuel storage tanks of retail gasoline stations. The OPW Vaporsaver system, fitted

with MTR's membranes, recovers gasoline vapors and returns them to the storage tank.

Hydrocarbon emissions are reduced by 95-99%.

Air from the gas station dispenser is collected and sent to the gasoline storage tank. When

the pressure in the tank reaches a preset value, a pressure switch activates a small

compressor that draws off excess vapor-laden air. A portion of the hydrocarbon vapors

condense and are returned to the tank as a liquid. The remaining hydrocarbons permeate

the membrane and are returned to the tank as concentrated vapor. Air, stripped of 95-99%

of the hydrocarbons, is vented. In addition to eliminating hydrocarbon emissions, the unit

pays for itself with the value of the recovered gasoline.


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Gasoline Vapor Recovery

Membrane Vapor Recovery Units (VRU) For Tank Storage

The Membrane Vapor Recovery Units(VRU) For Tank storage make it possible to recover

more hydrocarbon vapors than any current carbon-based systemIt efficiently processes

the relatively high organic concentrations found in gasoline vapors generated in storage,

unloading/loading and other processes involving evaporation and it is not hampered by

media saturation or regeneration issues.

This process is composed of three parts: The main operations of the process are

compression, and membrane vapor separation and pressure-swing adsorption. According to

different discharges requirement the third part can be selected.

Firstthe gasoline vapors is compressed by compressor. Then, it is cooled in a condenser.

The majority of oil gases component is condensed by low temperature water in the cooler,

and returns to the storage tank as the recycled gasoline after separating from the gas phase

in the separator. The Saturated gas leaving the separator enters the membrane section

where it passes across the surface of the MTR composite membrane. As a result, the

membrane feed is separated into a hydrocarbon-enriched permeate and a purified gas. The

permeate stream is recycled to the suction of the compressor, and the purified gas goes to

adsorber. Pressure swing adsorption process has two adsorbers. The purified gas can be

directed to either or both of two adsorption beds:one is for adsorption while the other one is

for desorption using the cacuum condition created by a vacuum pump.The desorbed vapor

and the hydrocarbon-enriched permeate returned to inlet of the compressor.


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Membrane Vapor Recovery Units For Tank Storage

Benefits of membrane Vapor Recovery Units (VRU)

High on-stream factor (typically > 98%)

Minimal or no operator attention

Highly flexible and treat a wide range of different hydrocarbons

Small footprint, low weight (Platform Applications)

Lower capital and operating costs

Simple passive system


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