The water treatment plant built by the Brown Boveri / Sulzer consortium delivers up to 1300 m³ of industrial water per hour from river water for the process and cooling needs of the refinery. Mutually coordinated process control loops ensure a continuous flow from the abstraction of raw water from a river through to the entry of clarified water into the refinery. The pump sets are automated only so far as uninterrupted operation requires.
Purpose and setting
The plant formed part of the overall project for a large NIOC oil refinery near Isfahan. Brown Boveri led the consortium and delivered a turnkey water treatment plant supplying the cooling and process water the refinery needed.
Raw water is abstracted from the Zayandeh Rud at the edge of Isfahan and pumped to the treatment plant 600 m away. From there, high-pressure pumps deliver 1300 m³/h of treated industrial water through a 25 km pipeline to the refinery.
The plant was designed so that its capacity could later be increased by a further 450 m³/h. That additional volume was to be treated to drinking water quality and delivered through a filter plant still to be built, over a separate pipeline, to the thermal power station planned next to the refinery.
Delivery into the treatment plant
Two pipelines of 800 mm diameter each carry river water by gravity through coarse screens into the collection chamber of the raw water pump station, 80 m away. From there three raw water pumps (P1–3) take over, delivering through a 600 m pressure line into the treatment plant. Each of the three pump sets has a capacity of 240 l/s and a drive rating of 200 kW. They are switched in by hand according to demand — which is fairly constant — and normally switched out by hand as well, guided by the pump discharge pressure indication (PAH 101) or the level in the control tank (LAH 105, TK 8). Should the operator's command fail to come, those same instruments trip an emergency shutdown through their maximum contacts when preset limits are reached.
A control valve (LRCV 101) at the inlet to the treatment plant regulates the delivered flow — up to a maximum of 1700 m³/h — to hold a constant level in the control tank (TK 8). A surge relief system protects the pressure line and the raw water pumps against water hammer caused by vacuum formation.
The treatment process
Before entering the five parallel reaction tanks (R 1–5), the raw water is dosed from the chemicals plant with:
- chlorine (Cl2) for disinfection;
- ferric chloride (FeCl3) to flocculate colloidal particles;
- lime milk [Ca(OH)2] to set the pH optimally and assist flocculation.
The carrier medium for the chemicals is clarified water branched off downstream of the control tank, its quantity regulated in proportion to the raw water flow measured at FRC 102.
Agitators in the reaction tanks build flocs large enough to settle well. Sludge returned from the settling basins (S 1–5) by the sludge recirculation pumps (P 6–11), together with polyelectrolyte dosing, further increases floc concentration. A connecting pipe feeds the raw water with its flocculated impurities into the settling basins from below, giving equal water levels in basins and reaction tanks and therefore a slow upward flow. The flocs settle on inclined lamella elements which multiply the effective settling area, then slide down them under gravity.
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Source
Wasseraufbereitung für eine Erdöl-Grossraffinerie. In: Brown Boveri Mitteilungen 6-80, p. 334.
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