FORM 2
THE PATENTS ACT, 1970
(39 OF 1970)
THE PATENTS RULES, 2003
Provisional/ Complete specification
[See section 10 and rule 13]
1. Title of invention:
"RECOVERY OF HEATER TREATER GAS FOR FUEL GAS PURPOSE"
2. Applicant(s):
Name Nationality Address
Oil and Natural Gas India IOGPT, Phase - II, Panvel -
Corporation Ltd. 410221, Navi Mumbai,
Maharashtra, India.
3. Preamble to the description:
The following specification particularly describes the invention and the manner in which it is to be performed.

RECOVERY OF HEATER TREATER GAS FOR FUEL GAS
PURPOSE
BACKGROUND OF THE INVENTION
1.0 FIELD OF INVENTION:
The present invention relates to a new energy efficient process for saving of natural gas in a Group Gathering Station of onshore oil and gas treating facilities.
2.0 DESCRIPTION OF THE PRIOR ART:
2.1 Present Practice
The well fluid (oil, gas and water) from the wells is received at the manifold of the processing installation called Group Gathering station. The well fluid is separated into gas and liquid phase in the two phase separators. Depending on the inlet pressure, separation is done in single stage or in multiple stages.
The gas produced from the separators is scrubbed in a gas scrubber to remove the liquid entrainment from the gas. The gas is then diverted to the consumers or to the gas grid for gas lift purpose. It is also used internally within the installation as a fuel gas in the heater treaters.
The liquid produced from the separators, consisting of oil and water, is taken into the heater treaters for removal of water. The water is removed from the liquid by first heating the liquid and then in the electrostatic chamber.
The heater treater is operated in the pressure range of 1.5 kg/cm2 to 2.5 kg/cm2 and temperature range of 60-80 deg C. In the heater treaters, gas produced from the separators is used as fuel for heating the crude. Fuel gas

is provided from the fuel gas grid (5 - 6 kg/cm2) through a pressure reduction valve located near the fuel gas scrubber. Two gas fired burners with operating pressure of 0.5 - 1.0 kg/cm2 are provided in the heater treaters for heating.
The dehydrated crude oil from the heater treaters is stored in storage tanks and pumped to the consumers. The effluent water from the heater treaters is collected in wash tanks and disposed off through effluent disposal pumps for injecting into subsurface or to effluent treatment plant. High calorific value hydrocarbon gas evolved from the heater treaters during dehydration of the liquid emulsion is sent to the flare.
2.2 Area of concern in the existing process
While dehydrating the liquid in the heater treaters due to heating, the hydrocarbon gas is evolved which is presently being flared into the atmosphere. Flaring of this gas results in wastage of hydrocarbon gas simultaneously leading emission of green house gases into the atmosphere: Flaring of gas in an oil and gas installation is a point of concern. It will be beneficial if flaring can be avoided by recovery of this gas.
An innovative and energy efficient process system has been designed by making modifications in the existing process system in order to reuse the gas generated from the heater treaters and consequently reduce the carbon footprint of an installation .
3.0 DETAILED DESCRIPTION OF THE INVENTION:
3.1 Re-routing of heater treater gas to burners of heater treaters:
In the present group gathering station of oil and gas treating facilities, it has been observed that a significant quantity of hydrocarbon gas generated from the heater treaters is being flared. In view of energy and environment

concerns, this gas which is being wasted can be fruitfully utilized as a fuel gas within the installation.
The quantity of the gas generated from the heater treaters mainly depends on its operating temperature and pressure, API gravity (American Petroleum Institute gravity) of oil and operating pressure of the inlet separators.
In a typical onshore oil and gas installation handling about 1400 m3/day of liquid having 23.86 American Petroleum Institute ("API") gravity oil and 80,000 rn3/day of gas with separator operating pressure of 5.0 - 6.0 kg/cm2, approximately 1900 m3/day gas is evolved from the heater treaters. The heater treaters are operated at a temperature of 60 - 80 deg C & at a pressure of 1.5 to 2.5 kg/cm2.
The requirement of fuel gas in the heater treaters of a typical installation is to the tune of 10,000 m3/day which is met from the gas produced from the separators at 5.0 - 6.0 kg/cm2. The gas from the separators is sent to the burners at 0.5 to 1.0 kg/cm2 through a fuel gas line with the help of a pressure reducer. The gas evolved from the heater treater in a typical installation has been observed to contain approximately 26 % of methane and rich in heavier hydrocarbons. FIG. 1 shows a schematic diagram of the existing process system ln a typical Group Gathering Station.
An appreciable quantity of gas can be saved by doing process modifications. The produced gas from the separators at 5.0 - 6.0 kg/cm2 is reduced to a pressure of 0.5 - 1.0 kg/cm2 for fuel gas purpose through a pressure reducing valve (PRV). In the modified scheme, the gas generated at a pressure of 1.5 -2.5 kg/cm2 from the heater treater will be taken into the fuel gas line which is at a lower pressure of 0.5 - 1.0 kg/cm2. The heater treater gas will enter into the inlet of fuel gas scrubber after the PRV in the fuel gas line instead of flaring. The gas evolved in the heater treaters can be rerouted into a fuel gas

scrubber through a pressure control valve and a restricted orifice installed on the recycle gas line for flow control. A pressure control valve has to be installed on the flare line to prevent over pressurization of the vessel. FIG. 2 shows a schematic diagram of the modified Group Gathering Station.
The above innovative process modification will result in reduction in flaring of gas from heater treaters and will also reduce emission of carbon dioxide into the atmosphere. Gas thus recovered from flaring and used as a fuel gas will reduce the quantity of gas drawn from the fuel gas grid making more gas available for sale to consumer. In a typical installation, approximate 20% of the fuel gas requirement can be met by recycling of heater treater gas.
4.0SUMMARY OF THE INVENTION
Presently in an oil and gas processing installation, the gas generated from the heater treater is sent to flare while dehydrating the liquid at 1.5 - 2.5 kg/cm2 and 60 - 80 deg C. The invented process uses the gas evolved from the heater treaters as fuel in the burners of the heater treaters by making use of the pressure difference between the heater treater and fuel gas pressure to heater treaters. The invention helps to utilize the gas generated from the heater treaters in the heater treaters itself.
The gas evolved in the heater treaters is routed into the fuel gas line through pressure control valves. This saves the heater treater gas from being flared and subsequently reducing the greenhouse gas emissions in the environment. Re-utilisation of heater treater gas as a fuel gas gives a scope for revenue generation by selling the extra gas made available.

5.0 BRIEF DESCRIPTION OF THE DRAWINGS:
The above and other objects, features and other advantages of the present invention will be more clearly understood from the following drawings, in which:
1) FIG. 1 is a diagram of conventional Group Gathering System
2) FIG. 2 is a schematic diagram of Group Gathering System with modifications.

WE CLAIM:
1. Routing of hydrocarbon gas evolved from the heater treaters and its use as a fuel gas for heater treaters will result in saving of hydrocarbon gas.
2. The recovery of the heater treater gas instead of flaring reduces greenhouse gas emissions.