Operation procedure illustration of FWG plant SASACURA KM30 (figure below)

 Before starting, the following valves are to be closed:

- Inlet and outlet valves for jacket cooling water of heat exchanger

- Vacuum breaker valve (V4)

- Outlet valve for distillate pump (V1)

- Feed water inlet valve for heat exchanger (V2)

- Bottom blow valve (V3)

- Other valves and cocks connecting to the atmosphere

Starting up

1) Open the outlet and inlet valves of condenser cooling water and lead cooling water into the condenser.

2) Fully open the ejector pump inlet valve as well as the cooling water overboard discharge valve. Start the ejector pump and check that the condenser air outlet valve (V19) functioning correctly.

3) Open the feed water adjust valve (V2) and lead sea water into the heat exchanger (pressure 0.04 to 0.06 MPa). Feed water quantity can be seen by the reedings of the compound gauge in front of the feed water orifice. Control feed water quantity within range of green belt shown in the compound gauge.

a

b

The FWG plant with shall-and-tube type of heat exchangers SASACURA KM30 operating procedure illustration

a – front view, b – backside view 

4) Start the chemical injection unit

5) Check the degree of vacuum in evaporator. When the vacuum in the generator become about 70 cmHgV (-0.092 MPa), open the inlet and outlet valves for jacket cooling water is to be opened slowly lest the heat exchanger should be overheated suddenly.

6) The air vent cock (V5) at the upper part of the heat exchanger shell should be opened whenever jacket cooling water passes through the heat exchanger and should be closed after confirming that the air in the shell is completely discharged.

7) Power on the salinity alarm in order to check purity of the fresh water.

8) When the distillate freshwater comes up to the sight glass of the suction pipe of distillate pump, start the distillate pump and regulate the water quantity by the outlet valve of the pump (V1). If there is not abnormality on the discharge pressure of distillate pump, the level need not always be fixed (normal discharge pressure is 0.14…0.22 MPa).

Fresh water quantity is increased as the sea water temperatures falls after adjusting to the fixed freshwater quantity. Naturally water level at the distillate pump suction side increases, produced water stays inside of the condenser, the effective heating area of the condenser decreases, evaporation quantity decreases, accordingly, the operating condition will be naturally balanced.

 

Regulating the capacity

The capacity (quantity of produced distillate) of the FWG is regulated by increasing or decreasing the quantities of jacket cooling water to the heat exchanger.

The capacity of the plant is now measured by means of the integrated flowmeter, the quantity of the jacket cooling water shall be regulated by the by-pass valve to the fresh water cooler until the plant produces its normal capacity.

In case that the temperature of the jacket cooling water is lower than the prescribed one, the flow quantity passing through the heat exchanger shall be increased more.

The supply of cooling sea water to the condenser is regulated so that the cooling sea water temperature rises about prescribed value when passing through the cooling tubes of the condenser.

The evaporation temperature should be about 45 ˚C to 60 ˚C.

Evaporation temperature may become much lower than suitable range when ship sails in low sea water temperature area.

In such case, evaporation temperature must be raised by means of their adjusting “vacuum adjust valve” (V7) on air extraction line, or reducing condenser cooling sea water flow rate.

If the evaporation temperature is too high which may occur at high cooling sea water temperature, the quantity of cooling sea water to the condenser is increased which will make the evaporation temperature drop.

Too high evaporation temperatures increase the risk of scale formation in the tubes of the heat exchanger, and too low evaporation temperature will be owing to the resulting great vapor volumes mean a risk that sea water drops are brought with to the condenser resulting in fresh water with a too high salt content.

 

Stopping

When the vessel comes close to a port, land or estuary the FWG is desirable to be stopped because at such places the sea water may be heavily infected with bacteria, and there is a risk that bacteria can be mixed in the generated distillate.

Before the FWG is stopped the by-pass valve for the jacket cooling water should first be opened fully.

1) Close the inlet and outlet valve of the heat exchanger.

2) Stop the distillate pump. Fully close the distillate pump outlet valve (V1).

3) Run the ejector pump for at least 30 minutes to supply feed water to the heater to cool down the heater.

4) Stop the chemicals injection unit.

5) Power off the salinity alarm.

6) Fully close the feed water adjust valve (V2).

5) Stop the ejector pump.

6) Close the outlet and inlet valves of the condenser.

7) Open the vacuum breaker valve (V4) to turn the vacuum in the evaporator to the atmospheric pressure.

8) Close the overboard discharge valve and inlet valve of the ejector pump.

Don’t open the bottom blow valve (V3) in order to make atmospheric pressure because sea water in the heat exchanger may be blown up and damage the deflector etc.

In case that the plant is stopped for a long time, the heat exchanger is emptied of sea water by opening the bottom blow off valve at the bottom of the heat exchanger.

 

Attention during operation

1)  Regulating the capacity

Any regulation of the capacity of the FWG should be effected by regulating the amount of jacket cooling water to the heat exchanger. Although when the tubes are clean, the FWG will be able to produce freshwater in excess of its rated capacity, we recommend that you will operate the plant at the prescribed quantity of fresh water or less as production in excess hereof can involve the risk of scale formation.

2) The condenser

In order to condense all generated vapor in the heat exchanger, cooling sea water, as cold as possible should be flowed to the condenser and also should be checked temperature difference of cooling sea water between inlet and outlet of condenser for regulating the amount of cooling sea water. In case excess cooling sea water should be supplied, turbulent corrosion may possibly caused due to too high velocities in the cooling tubes of condenser. On the contrary, when cooling sea water is short, the capacity of produced fresh water should decreased because of short cooling performance.

Calculation for quantity of cooling sea water of condenser:

 

, (t/h)

D – capacity of produced distillate (T/day)

t₁ – inlet temperature of condenser

t₂ – outlet temperature of condenser

Q – capacity of cooling sea water

 

It is requested to adjust outlet valve of condenser in case that capacity of cooling sea water is exceeded more than value specified in heat balance.

Maximum quantity of cooling water of KM 35 type 90 t/h.