طرق معالجة الاكسجين الكيماوى المذاب لمياه الصرف الصناعى الناتج من ابار الغاز الطبيعى والبترول ومصانع البتروكيماويات بالمؤكسدات

The chemical treatment for decreasing cod of natural gas waste water by oxidants

Gas well production fluid normally consists of natural gas and gas condensates which are separated from water by physical techniques.

The separated water stream is referred to as “produced water”.

Produced water contains dispersed and soluble organic hydrocarbons.

The dispersed hydrocarbons can be found as fine droplets contained in water in the form of emulsion.

The volume of produced water from gas field is less than in oilfields.

In gas fields, the produced waters are mixture of well formation water and condensed water

Their chloride content varies from almost those of fresh water to salty formation water with chloride concentration about 14 times that of seawater which is a major contributor of toxicity

A wide range of gas treatment chemicals is used in gas fields including ethylene glycol, and tri ethylene glycol which are mostly discharged in produced water.

Volatile components concentrations in produced water from gas fields are higher than those in produced water from oilfields.

Environmental effect of produced water can occur in all regions where oil and gas have been produced

Dispersed oil and droplets rise to the surface of water and increase the biochemical oxygen demand (BOD) of the affected water

Volatile and/or toxic compounds evaporate.

These materials are consistently toxic

Also, due to the large volumes of water produced in the oil and gas fields, possible re-use of the treated water has been taken into consideration during recent years.

Wastewater treatment processes are being developed to reduce the amount of hydrocarbons in the produced water to acceptable levels.

Conventional phase separation techniques will not remove the water soluble organics from the aqueous phase.

Thus, various biological and chemical oxidation methods have been used to treat the produced water of oil and gas industries.

chemical oxidation of hydrocarbons in produced water separated from gas stream of Gas Refineryhas been carried out.

Among available oxidants three oxidation agents with different oxidation power (ozone, hydrogen peroxide, and calcium hypochlorite) has been used to decrease the chemical oxygen demand (COD) of the produced water.

Oxidation power of some oxidation reagents

Oxidation species Oxidation power

Hydroxyl radical 2.80

Ozone 2.07

Hydrogen peroxide 1.77

Permanganate 1.67

Chlorine dioxide 1.50

Hypoiodous acid 1.45

Chlorine 1.36

the characteristics of the composite sample of produced water after oil separation in API unit.

All experiments were carried out using this sample.

Three oxidants, hydrogen peroxide, ozone and calcium hypochlorite, which present different oxidation power, were selected for oxidation of dissolved and dispersed hydrocarbons.

Hydrogen peroxide

is a strong oxidant readily applied to wastewater treatment in the past.

Hydrogen peroxide

has been found to be effective in degradation of compounds or treatme

nt of real wastewaters requiring less stringent oxidation conditions but applications to complex mixture of effluents like dyes, textile industry effluent, hetero aromatics and the present produced water need to be explored.

The stoichiometry amount of hydrogen peroxide for complete COD removal of produced water was calculated as 570 mgL–1 .

Oxidation of produced water by 600 mgL–1 of hydrogen peroxide after 4 hours reaction decreased its COD to the level of 228 mgL–1 which corresponds to 15% degradation of organic materials

low degradation rate of organic materials in the produced water.

A major problem

encountered with the application of hydrogen peroxide alone for wastewater treatment applications are very low rates for applications involving complex materials.

Moreover, stability of H2O2 remains a question, as the catalytic decomposition agents present in effluents compete with the pollutants

Ozonation

of produced water for 1 hour at pH of 7.2 ended to COD value of 203 mgL–1 (i.e. 12% COD removal).

Increasing pH of the water to 10, improved treated water quality (to COD of 192 mgL–1 ), which indicated higher ozonation efficiency (29%) of the produced water at higher pH values.

Higher pH values enhance the formation of hydroxyl radical which is a strong oxidation in the presence of ozone.

Thus, it appears that the use of ozone alone is not feasible for the treatment of complex compounds in the produced water

and combination with other advanced oxidation techniques seems to be a better alternative.

Maximum COD removal efficiency was achieved for calcium hypochlorite oxidant.

Employing concentrations of 300, 500, 1000 and 7100 mgL–1 of calcium hypochlorite, showed COD removal in the range of 36-70%

The final COD values were obtained as 80-173 mgL–1 .

In spite of lower oxidation power of chlorine, the results show the higher efficiency of calcium hypochlorite in degradation of organic materials within the sample.

This might be due to the structure of the water pollutants. It was found that calcium hypochlorite is cost-effective and easy to use for chemical oxidation of the produced water.

The drawback of this process is the residual chlorine in the water which should be eliminated for further use of the water.

the kinetic studies of calcium hypochlorite oxidation at the concentrations of 500 and 7100 mgL– 1.

The results revealed that the reaction was completed within 30 minutes at concentrations higher than 500 mgL–1 .

Fenton Oxidation of Natural Gas Plant Wastewater

raw natural gas extracted from reservoir contains impurities that must be removed before it can be used.

The raw natural gas which primarily consists of methane also contains varying amounts of other components such as heavier gaseous hydrocarbons (ethane, propane, butane etc.), acid gases (carbon dioxide, hydrogen sulfide, mercaptans etc.), water (vapor and liquid) and liquid hydrocarbons.

After the treatment, the processed natural gas will contain almost pure methane and it is used as fuel by residential, commercial and industrial consumers.

Amine gas treating, also known as gas sweetening and acid gas removal, refers to a group of processes that use aqueous solutions of various alkanol amines to remove hydrogen sulfide (H2S) and carbon dioxide (CO2) from natural gas.

This treating unit is commonly used in refineries, petrochemical plants, natural gas processing plants and also some other industries.

The first alkanol amine commercially available for acid gas treatment was tri ethanol amine (TEA).

Since then, the other members of alkanol amines were introduced in the market and evaluated as possible acid gas absorbents

Various amines are now available such as mono ethanolamine (MEA), di ethanolamine (DEA), di iso propanol amine (DIPA), methyl di ethanol amine (MDEA) and TEA.

Characteristics of the wastewater

Characterization Amount

pH 8.67

Chemical Oxygen Demand 17, 028 mg/L

5-day Biological Oxygen Demand 909 mg/L

Total Organic Carbon 3,337 mg/L

Total Suspended Solid 4,517 mg/L

Total Volatile Solid 640 mg/L

Total Nitrogen 916 mg/L

Oil and Grease 622 mg/L

COD removal for same initial COD concentration (17000 mg/L) and ferrous sulfate dose (23.97g) in 500 ml reaction mixture but with different H2O2 dose [43, 64.5, 86, 108 and 130 ml; 30% w/w) are used to calculate the initial rate of degradation.

The reduction of COD over thirty minutes was used for calculation of [rs]0.

Fenton’s oxidation to degrade natural gas plant wastewaters which primarily consist of non bio degradable organic compounds has been studied and proved to be efficient.

With initial COD concentration of approximately 17,000 mg/L, the optimum H2O2/Fe2+ molar ratio is found to be at 10 and wastewater’s initial pH of 3.

The highest COD removal achieved was 73% which can be further reduced in biological treatment system due to the formation of carboxylic acids.

The proposed rate constant fitted reasonably well and found to be applicable to predict the final COD at different conditions.