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particle concentrations 
Electrostatic precipitators 
- High efficiency - 
High-cost 
equipment 
Fabric filtration 
- High efficiency 
- Moderate-cost equipment 
- Can be damaged by high 
temperatures or water 
Scrubbing systems 
- High efficiency 
- Moderate-cost equipment 
- Control also SOx emissions 
- Corrosion problems 
- Wet slurry production 
- Water pollution 
Table A-2-2: Comparison of SOx-removal techniques 
2.5. Carbon dioxide 
The major gas emitted during combustion is obviously carbon dioxide. These emissions have 
generally to be minimised due to actual context. Frequent measures to reduce carbon dioxide 
emissions in plants are Energy Management Systems (tool used to control and optimize the 
energetic performance) and cogeneration (use of heat engine to produce both electricity and 
heat). A good optimization of processes is a way to recover all energy available, thus reducing 
CO
2
generation. 
Conclusion 
Many methods exist to reduce emissions from process heaters and boilers. Usage of a cleaner 
fuel, better combustion, low-NOx burners, or postcombustion control techniques contribute 
all to emit less pollutants into the atmosphere.
3. Blowdown systems
1,14,15 
Petroleum industry process units are equipped with a collection unit called the blowdown 
system. It allows the safe disposal of liquid and vapor hydrocarbons that are vented in 
pressure relief valves or drawn from the unit. This system can also be used to purge the unit in 
case of shutdowns. Blowdown materials are partly liquid and partly vapor. The liquid cut is 
either recycled into the refinery or sent to the waste water treatment. The vapor cut is either 
recycled or discharged directly to the atmosphere or flared. When discharged directly to the 
atmosphere, emissions consist principally in hydrocarbons. When flared, sulfur oxides are 
emitted. The emission rate of the blowdown system depends on the amount of equipment 
considered, the frequency of discharges, and the blowdown system controls. 
3.1. Emissions to the flare 
Flaring is a safety measure used in petroleum industries to ensure that gases are safely 
disposed of. A flare is a device that burn hydrocarbons emitted from emergency process vents 
or pressure relief valves. It is usually assumed that flares have a combustion efficiency of at 
least 98%.

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14
The combustion reaction is: 
C
x
H
y
+ (x + y/4) O
2
→ x CO
2
+ y/2 H
2
O 
Principally carbon dioxide is emitted from flares, but also organic compounds and carbon 
monoxide, NOx, SOx and soot. 
It is actually impossible to estimate flare emissions, however, several measures can be 
adopted to minimise these emissions: 
- Use of efficient flare tips, and optimization of the size and number of burning nozzles. 
- Maximization of flare combustion efficiency by controlling and optimizing flare 
fuel/air/steam ratio. 
- Minimization of flaring from purge without compromising safety, through measures such as 
purge gas reduction devices, flare gas recovery units, inert purge gas. 
- Installation of high integrity instrument pressure protection systems, where appropriate, to 
reduce over pressure events and avoid or reduce flaring situations. 
- Minimization of liquid entrainment in the gas flare stream with a suitable liquid separation 
system. 
- Implementation of burner maintenance and replacement programs to ensure continuous 
maximum flare efficiency. 
3.2. Liquid emissions 
In order to minimize liquid emissions, it is important to recycle as much as possible drained 
liquids. If recycle is not possible, segregation of process drained liquid from relatively clean 
water can reduce the quantity of oily sludge generated. Moreover, it is easier to recover oil 
from smaller and concentrated streams. 
4. Wastewater 
12,20 
Wastewaters from petroleum industries are various. They can be process waters such as crude 
oil desalting waters or sour waters from hydrocracking or hydrotreatment processes, general 
effluents such as drained oily waters, washing waters and finally spent caustics. In order to 
meet quality requirements about wastewater releases, the best way is to segregate these 
different waters. In this chapter, common techniques for wastewater treatments in refineries 
are shortly described and then, best management practices for process wastewater are given. 
4.1. Wastewater treatment techniques