Analysis of gas recycling systems sent to the burner

Dissertation for receiving a master's degree,,M.Sc,,

Energy Systems Engineering - Energy Systems

One ??of the most important issues related to the environment in the oil, gas and petrochemical industries is the proper disposal of waste hydrocarbon gases in industrial units and complexes. One of the most common methods available for the safe disposal of these gases is burning them in flares and releasing them into the environment. Optimizing energy consumption and reducing environmental pollutants is one of the basic concerns of these industries, and since the main way of energy loss in refineries in the country and in general all centers with flaring systems such as: oil wells, oil and gas refineries, process units, chemical plants, waste incinerators, etc., is this flaring system and mainly the largest amount of environmental pollutants such as CO2 is also emitted from this system, attention to optimization The performance and improvement of this section is very important.  A significant part of the gases sent to the flares are compounds such as: natural gas, ethylene, propylene, four-carbon cuts and hydrogen, which are very valuable from an economic point of view. With the help of designing a special gas collection and recycling system, the amount of flaring of an industrial unit such as a refinery can be significantly reduced and in this way the gases that were burned until now are collected and then converted as feed for process units and gas fuel for the systems in the unit. Following this process, the pollution caused by the burning of gases will be significantly reduced. Despite the many economic benefits of using flare gas recycling systems, the operationalization of this idea, especially in the existing process units in the country, is faced with certain complications in relation to the required technologies, such as condensation systems (for example, a compressor with a liquid ring), and on the other hand, the economic inefficiency of using these expensive technologies to recycle gases that are commonly burned as waste. Therefore, according to the above-mentioned cases, the review of existing systems for the study of flare gas recycling Based on common and accessible technologies, a flare gas recovery system was developed that has an acceptable performance in terms of economics. In this plan, with the help of designing a special compression system using gas compressor technology and common separation and purification technologies, the amount of flaring can be significantly reduced and the possibility of separating and recovering valuable compounds from flare gas is provided in the research present. Presenting a practical and justifiable economic method of condensation with gas ejector technology in a suitable system for the recovery of gases sent to flares in process centers with relatively low amounts of flaring and with a low percentage of methane, regardless of the complexity of the structure of the studied unit, is the main achievement of the present research. First, the gases sent to the flare are gases with a significant economic value, and the second point is the harmful environmental effects caused by the combustion of said gases [1]. Our beloved country, Iran, with huge oil and gas reservoirs and extensive facilities in the upstream, midstream and downstream sectors, transforms significant amounts of valuable gases in flares into harmful gases for the environment. Although extensive measures have been taken to reduce the losses of this national capital in the country, there is still a need to provide appropriate solutions in this field, which can be examined in a comprehensive plan. Therefore, managing the production and reduction of flare gases is a suitable platform for carrying out scientific, research and practical activities not only in the country but also in the whole world. It is petrochemical and so far various methods have been investigated and used both in the initial design phase and in the modification phase of the existing units.One of the most important issues related to the environment in these industries is the proper disposal of waste hydrocarbon gases in industrial units and complexes. One of the most common available methods is releasing and burning these gases. There are different methods and equipment to do this, which can be used according to the different nature of these materials.  The most common type of these equipments are flares.  Flares are suitable equipment for the safe disposal of waste gases by combustion and releasing them into the environment [2].

Fler is a chimney or an extended vertical pipe that is used as one of the essential parts in oil wells, refineries, petrochemicals, chemical plants, waste incinerators and other process units to burn waste gases and liquids, flammable and toxic, and can prevent fire hazards. Prevent fires, explosions and injury to employees. In fact, the flare converts flammable, toxic and corrosive vapors into less harmful compounds and is one of the main methods of securing industrial devices against increased pressure.[3] and [4].

Flaring is a process of burning and combustion in which organic substances and excess combustible gases are sent from all parts of the unit through a network of pipelines to an area with a suitable distance from the operating units and burned in a controlled manner before they cause problems for the facilities.  Flares always produce heat and sound during operation.  The amount and type of gases emitted from the flare to the environment depends on the combustion efficiency and the type of gases sent to the flare [5].

The flare system generally burns the received gases in three different operating conditions of the unit:

1) Normal factory conditions: In this case, the gases released from some processes are burned in the flare along with the exhaust gases and usually without combustion. Smoke, sound and light follow. Combustion products in these conditions are mostly water vapor, carbon dioxide and sulfur dioxide. In these conditions, it is possible to recycle some gases after re-compression as fuel.

2) Turbulent conditions of the unit: these conditions occur during the start-up or complete stop of the plant and the volume of gases sent to the flare is more than normal conditions.

3) Emergency conditions of the unit: when accidents such as technical malfunctions of the device or power cuts occur, some of the gases are Unsolicited sent to Fler. Because in this case, the adjustment of fuel and air ratio is inappropriate, so black and smoky flames are created. Emergency situations may occur for various reasons, some of which are: [1]

Change in incoming feed

Technical failure of equipment

Improper maintenance and repair

Human errors

Deviation from operation procedure

Power cut

Operation exceeding design capacity

Although every chemical process such as refinery and petrochemical processes are required to use a flare system for various reasons to ensure the safety of workers and equipment, solutions can be provided to minimize the amount of current sent to the flare. The solutions to reduce flaring in each of the three main parts of the flare system can be presented and implemented as follows:

1) Process part: reducing the production of flare gases by improving the process conditions and preventing leaks in equipment and connections

2) Collection network: recovery and reuse of produced flare gases based on its specifications

3) Flare system: modification of the flare system including the equipment, their performance and control and monitoring systems

In Iran, the inadequacy of projects to reduce, collect and recycle the gases sent to the flare causes unnecessary burning of gas. The methods and solutions that have been presented up to now to reduce or recover the gases sent to the flare are mainly focused on the modification of the gas producing units sent to the flare.