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Introduction
In 1997 ACWA were commissioned to provide a unique drinking water process for a Saudi Arabian Oilfield Development Site. A £2M Hydrogen Sulphide Stripping and Reverse Osmosis Filtration Plant was supplied, installed and commissioned by ACWA to provide drinking water for more than 10,000 resident construction workers and ARAMCO staff at the ARAMCO refinery development site in Shaybah – a remote desert region of Saudi Arabia, known as the Empty Quarter (145km south of the Arabian Gulf).
| Description |
Raw WaterCharacteristics Average |
Raw Waterafter pretreatment |
Product |
| Flow m3/day |
3 x 125m3/h |
3 x 125m3/h |
3 x 125m3/h |
| TDS |
15,000ppm |
20,000ppm |
<500ppm |
| Hydocarbons |
Up to 3ppm |
nil |
nil |
| Hydrogen Sulphide |
Up to 200ppm |
nil |
nil |
| pH |
8 |
8 |
6 |
| Temperature °C |
Up to 55 |
Up to 55 |
Up to 55 |
The Shaybah site was primarily concerned with the construction of plant for the production of oil and gas products, but also the building of roads, an airstrip and airport, housing, shops and other projects in oppressive daytime temperatures.
Pre-Treatment
Feedwater is pumped from boreholes deep beneath the Saudi Arabian desert into a break tank where, in the interest of safety, dissolved gases ‘flash off’ before discharge to the oil separation tank. After separation, the raw water is pH adjusted and pumped into eight H2S Stripping Columns (four streams of two in series) with individual loadings of 200 ppm H2S and flow rates of 54m³/hour per stream.
Each stripping column is designed to accept variations in liquid flow without affecting the optimum performance of the process. Stripping columns operate with a raw water inlet temperature of 55°C at atmospheric pressure and have 99.5% removal efficiency. Two towers in series provide removal efficiency in excess of 99.99%.
The ‘stripped’ water is dosed with 2ppm of sodium hypochlorite to ensure oxidation of any remaining H2S before being pumped to an intermediate storage tank.
On demand the water is pumped through sand filters (iron and manganese removal) and carbon filters (removal of residual free chlorine) to the reverse osmosis plants.
H2S Destruction
To meet stringent air quality emission standards, the stripping air, contaminated with H2S and hydrocarbons, is ducted to the thermal oxidiser for incineration. The Thermal Oxidiser, supplied and installed by ACWA AIR, is a horizontal cylindrical unit lined with refractory and ceramic fibre to protect the shell against thermal stresses during warm-up. A diesel-fired burner, mounted at the end of the unit, fires horizontally and provides the support fuel necessary for oxidisation of the waste stream. Contaminated air enters the ignition tube via the plenum chamber and is rapidly heated to 800°C as it enters the thermal oxidation zone where H2S and VOC’s are incinerated. The treated gases are then vented to atmosphere through a 30 metre high exhaust stack.
Reverse Osmosis
The 4 RO plants are capable of producing a total of 2650m³/d high quality drinking water which is continually monitored for conductivity, temperature, fl ow, pressure and pH. Each is an autonomous stream of treatment comprising:
- Acid dosing
- 5-micron Cartridge filtration
- Antiscalant dosing
- High pressure pumping
The pre-treated, conditioned water is boosted to 40 bar operating pressure and feeds the containerised RO plants. The system is designed to provide permeate recovery at a rate of 65% of the feedwater flow.
