Flash Type Evaporator Flashcards
The _______ consist of a welded rectangular box shell of copper nickel alloy mounted on a steel foundation.
Evaporator
The unit is divided up into _____ stages with the upper section containing the mesh separator, distillate trough and stage condensers.
Six stages
The lower section of the evaporator houses the _______ through which the untreated feedwater passes from one stage to the next.
Flash Devices (flash chambers)
An external pipe loop seal is provided to transfer the ______ from each stage to the following stage.
Distillate
______ are supllied in all these interstage distillate loop seals.
Orifice Plates
The following are conveniently mounted on the evaporator to provide a completely packaged unit.
- J/W feed heater
- Steam feed heater
- Distillate cooler
- Steam pressure reducing station
The following are all mounted on the evaporator foundation with their motors.
- Sea feed pump
- Brine pump
- Distillate pump
- Condensate drain pump
- Vacuum pump (with atmosheric air jet)
In a six-stage flash-type evaporator, the feedwater is heated in a series of ________ and then discharged in the first-stage evaporator.
Shell and Tube heat exchangers
This hot seawater passes through perforations in the first-stage feed assembly and then through a ______ where a portion flashes or vaporizes.
flashing device
The flashing of the feedwater occurs when the pressure in the flash chamber is lower than the _______ of the feed temperature.
Saturation Pressure
The vapor then rises through the mesh separator and condenses on the tubes of the ________.
First-stage condensor
The condensation occurs when the warm vapor contacts the tubes filled with cooler seawater, turning the vapor into water. It then becomes part of the product that collects in the _______.
Distillate Trough
The flashing and condensing cycle is repeated in the remaining 4 stages with decreasing _________.
Saturation Temperatures and Pressures
The quanity of fresh water produced depends upon the following:
- The quanity of seawater feed entering the first-stage flash chamber
- The total reduction of temperature of this seawater feed in the flashing process
Order of operation for a Six-Stage Evaporator
1st is the heat source, 2nd is seawater, 3rd is evaporation (boiling), 4th is vapor or brine, 5th is condensate (cooling) and 6th is distillate
If the evaporator is operating with jacket water as the heat source, a constant _______ must be maintained.
heat rejection rate
If the unit is operating with a steam feed heater as the heat source, a constant ________ in the steam line to the heater must be maintained.
steam pressure above the orfice plate
If the If the diesel engine is not operating. the seawater feed temperature is elevated to a desired level by the use of a steam feed heater. The heat source for this heater is _________.
Low Pressure
The __________ heats the water to the desired temperature before the feed enters the first-stage flash chamber.
steam feed heater
The ____ is used when the jacket water feed heater is not in operation.
steam feed heater
The ______ is of the U-tube type with the seawater on the tube side and steam on the shell side.
steam feed heater
The steam feed heater is furnished with the following:
- Valve
- pressure gauge
- thermometer
A two-pass unit with the feed water flowing through the tubes and the distillate flowing on the shell side.
Distillate Cooler
The purpose of the _______ is to lower the temperature of the distillate as the feedwater is heated.
Distillate Cooler
The ______ maintains the cooling temperature of the vacuum pump recirculating seawater.
The vacuum pump seawater cooler
The actual ________ is accomplished when the pressure in the first stage chamberis lower than the saturation pressure corresponding to the temperature of the seawater.
flashing of the feedwater
The driving force moving the feedwater is the ________ with each stage being at a lower pressure than the one before.
difference in pressure between the stages
When seawater is below ____ degrees fahrenheit, the vacuum required in the sixth-stage tends to be greater than the vacuum pump system can attain.
below 38 degrees fahrenheit
The vapor that is produced in the first-stage flash chamber passes through the _______.
Mesh Separator
Four salinity cells in the plant provide continuous monitoring of the water purity in the:
- Loop seal line between the first-stage and the second-stage distillate
- Distiilate pump discharge
- Air ejector drain line
- Seawater heater drain pump discharge
All salinity cells are read on a ______.
Salinity indicating panel
Salinity of produced water cannot go over ____ grains per gallon.
0.25 grains per gallon
The total distillate product of all the stages is finally drawn out of the sixth-stage distillate trough by the _____.
Distillate pump
The discharge from the distillate passes through the ______ where it is cooled by the incoming seawater feed.
Distillate Cooler
If the distiilate is within the specific purity as it passes through the the last salinity cell and the __________ , the three-way valve directs the distillate through the freshwater meter to the ship’s freshwater system.
feed temperature has been 166 degree fahrenheit or above for the last 15 minutes
The ______ is tripped by the dump relay if the salinity exceeds a specific purity or if the feed-temperature is below 165 degrees fahrenheit to the first-stage, then this distillate will be directed overboard.
Three-way Valve
Once the solenoid trip valve is tripped, the distillate continues to flow overboard until the solenoid trip valve is________.
manually reset after the purity and temperature have been restored
This valve is designed to automatically divert the output of the distilling unitwaste whenever the final purity of the distillate is unsatisfactory or when the feed temperature is below 165 degrees to the first-stage,
Three-Way Solenoid Trip Valve
The steam feed heater is vented to the shell of the first stage condenser through a ____ which includes a manual control valve.
1/2 inch line
The ______ is vented to the sixth-stage shell.
distillate pump suction
Saturated steam is supplied to the reducing station at _______.
35 psig
The saturated steam is then reduced in pressure from 35 psig to 5 psig by the ________.
steam pressure reducing valve
Then the saturated steam passes through an ______ which reduces its pressure to approximately 9.5 psia.
Orifice
It registers the quantity of freshwater being discharged from the distillate pump to the ship’s freshwater system.
Freshwater Meter
A ______ is provided to protect the system from high pressure due to malfunctioning of the distilling plant.
Relief Valve
There are _____ thermometers found within the distilling plant.
13
Shell thermometers are located in the following positions:
- First-stage
- Second-stage
- Third-stage
- Fourth-stage
- Fifth-stage
- Sixth-stage
Seawater feed line thermometers are located in the following positions:
- Inlet to sixth-stage condenser
- Inlet to J/W feed heater
- Inlet to first-stage flash chamber
Distillate line thermometers are located in the following positions:
- Outlet distillate cooler
- Distillate pump discharge
Aditional locations of thermometers are:
- Steam feed heater shell
- vacuum pump seawater inlet
The ______ gauges read from 30 inches of vacuum to 60 psig pressure.
Compound
The _______ indicating gauges read from 0 psig to 60 psig.
straight pressure indicating gauges
For normal evap operation the temperature will be from _____ to _____ degrees fahrenheit.
170 to 175 degrees fahrenheit
Due to hydrostatic leg of water in the vacuum gauge lines, during operation, allow the plant to stabilize for ______ to _______ minutes after gauges are bled.
15 to 30 minutes
The _______ automatically controls the feed rate.
feed temperature regulator
Feed temperature regulator should maintain an operating range of _____ to ______ degrees fahrenheit.
170 to 175 degrees fahrenheit
When water levels appear over halfway in the sight glasses that are mounted on the front of the evap, it indicates the plant is not operating satisfactorily. Possible cause are:
- Faulty operation of the brine overboard pump through the overthrottling of the brine overboard discharge valve
- Restricted flow of the feed between flash chambers
- Incorrect position of the brine loop seal butterfly valves
Gauge glasses are fitted on the suction lines to the brine, distillate and steam heater condensate pumps. A completely flooded gauge glass indicates:
- Pump is not functioning properly
- Pump discharge is throttled to high
This conditions should be remedied immediately.
Between ______ and ______ is ideal operating water level in the gauge glass.
bottom and halfway
Chemical feed treatment system correct mode of operation is ________.
3 PPM
Preliminary procedures for operating a flash type evaporator make sure all applicable valves are closed EXCEPT the following:
- Chemical feed pump discharge valve
- Air cooler drain valve
- Freshwater meter isolating valves
- Pressure gauge root valves
- Instrument air supply valves
- Pumps gland seal valves
- Steam pressure sensing valve
- for initial start-up only, Loop seal butterfly valves
- Condensate level controller reference leg valve
Steam Heater Operation
Throttle at __ to __ degrees and open the feed temperature regulator bypass valve.
25 to 50 degrees
Check the compound gauge on the sixth-stage shell. A reading of approximately __ inches of mercury should be indicated in 20 minutes.
27 inches of mercury
Adjust the steam pressure reducing valve to maintain _ psig above the orifice.
5 psig
The greatest amount of vacuum will always be in the sixth-stage and the least in the _____.
steam feed heater
Adjusting the condensate drain regulator
The valve stem packing gland nut should only be kept _____ and the packing will need to be lubricated occassionally.
finger tight
Adjusting Chemical Feed Pump
To maintain the chemical injection rate there are two options that can be used to adjust the injection rate:
- Adjusting the knob on the pump to different percent setting on the pump stroke
- Increase or decrease the solution strength.
What two types of cleaning are available for the evaporator?
Chemical and Mechanical
What is the prefferred method of cleaning an evaporator?
Chemical, because it is faster, more economical, more effective and less harmful
There are specific times you will want to perform a cleaning procedure on the evaporator, such as:
- When steam feedwater heater shell pressure decreases from approximately 11 inches Hg (vacuum) to 0 psig
- When heat transfer rates are noticeably lower by a capacity drop and the required feed temperature to the first-stage is not attainable.
- Depending on operating conditions, the period between cleaning varies.
Acid mixing tank, agitator, two 1 1/2-inch hoses and pump are required for _______.
Chemical Cleaning
