Sea exploitation

1. Seawater desalinization
Seawater desalinization is an important path for solving the shortage of fresh water. Presently, the seawater desalinization mostly use multi-flushing section flow, the industry equipments are constructed of seawater pre-treating equipments, heat releasing equipment, heat reclaiming equipment, salt water heater, demister and relevant pipelines, pumps, valves, etc. The seawater will first enter the conduit of the heat releasing equipments to be heated (to 40℃ within normal temperature), then most will be released, the pre-treating equipments will eliminate carbon acid (air) from the seawater and regard this seawater as replenishing seawater, and will mix it with concentrated seawater, after the concentration arrives at 1.7, these will enter the heat transfer pipe of the heat reclaiming part, here, the seawater is heated to 110℃ before it enter the heater, it will be heated to 120℃ with external steam heating, the heated seawater will be sent into canisters belong to reclaiming part, the canisters are divided to many sections inside by clapboards, the salt water will enter various sections, then the pressure and temperature will decrease continuously to make fast evaporation, the steam will pass anti-fog screen mesh, and condensate into fresh water outside the heat transfer tube.

The medium environment for seawater desalinization are mainly degassing seawater and fresh seawater; stainless steel has been successfully used in equipments of seawater desalinization including pumps, frames, axis, impellers, rods and the separator of evaporation tank, degassing equipments, etc., see the following table:

The application of stainless steel in seawater desalinization equipments

Name of technique equipment
USSR five function vertical long pipe type equipment
Evaporation separator
Degassing equipments

Multi section flushing equipment
Anti-fog equipment
Screw condenser heat transfer tube
Exhaust pipe of degassing equipment
Hull, axis, impeller, rods
Degassing salt water salt fog
Steam, non-condensate gas
non-condensate gas
Sea water, degassing salt water
Monel metal
Monel metal - 400

The heat transfer tubes for seawater desalinization occupy 40%-50% of equipment investment. To count with a 100,000 m3/day desalinization equipment, the heat transfer tubes contain copper alloy up to an amount of 2,200t. The heat transfer tubes play an important role in seawater desalinization. In the multi section flushing equipment, 10% of heat transfer tubes are used in heat releasing equipment, 87% are used in heat reclaiming equipments, and 3% are used in salt water heater. Presently, the stainless steel that can satisfy the above three requirements is the Cr-Ni-Mo-N stainless steel which is anti-corrosion of seawater, like the 00Cr22Ni17Mo3Nb and 00Cr22Ni13Mo5NNbV. In order to increase heat transfer effect, the tube is made as thin walled tube with wall thickness of 0.25mm; in order to enhance hardness, the smooth tube is made to be portrait bellows.

2. Sea hardware
Stainless steel has been widely adopted for sea exploitation machine and hardware that contact the seawater, see the following table:

Application of stainless steel in sea exploitation machine and hardware

Seawater pump
00Cr19Ni10, 0Cr17Ni12Mo2, 20 alloy, 17-4PH, 0Cr18Ni12Mo2 cast
Seawater valve
0Cr17Ni12Mo2 20 alloy (built-in fitting and valves)
Heat exchanger
0Cr17Ni12Mo2, 329J1, NTKR-4, 00Cr25Ni7Mo3WCuN, SAF2507, 00Cr22Ni17Mo3NNb
Connecting bolt
Casting 0Cr18Ni12Mo2
Metal pieces used on sea surface
0Cr18Ni9(pulley, wire rope), 0Cr17Ni12Mo2(bolts), 00Cr22Ni17Mo3NNb(high strength wirerope)
Metal pieces used in seawater
0Cr18Ni9, 1Cr18Ni12(wire rope), 00Cr22Ni13Mo2VNNb, 00Cr22Ni13Mo3NNb
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