Subsidence is accomplished by passing water through a basin or tank of such design that the velocity of the water is reduced to a point, to permit ___________.
__________ are chemicals, which cause the fine particles to gather together into a larger mass, which will settle out much more readily.
___________ is the further increase in size and volume of the precipitating particles and is done by gentle agitation of the water.
The coagulant, when added to the water, will produce a spongy substance known as _____.
A water _______ allows the coagulation and settling of suspended solids contained in water, to take place.
The clarified water is drawn off through a submerged collector pipe at the ______ of the upflow zone.
A ______ consists of a bed of porous material through which the water is passed, either by gravity or under pressure.
When filtering water, which will be used for boiler feedwater, __________ is preferred as the use of sand may result in the water picking up silica, which could deposit as scale, in the boiler.
Pressure gauges, are installed on the inlet and outlet lines and when the pressure difference between them reaches a certain value, usually from ___ to ___ kPa, it means that backwashing is required.
a. 5 , 10
b. 35 , 55
c. 100 , 200
d. 1 , 10000
If filters are used alone, then _________ are usually fed to the filter in order that the finer impurities are formed into larger particles that can be trapped by the filter bed.
Chemical external water treatment is accomplished using:
1. Zeolite softeners
3. Hot lime soda softeners
The sludge blanket aids in the removal of any ________ not already precipitated from the water.
Calcium sulphate, in particular, is the main scale forming constituent found in boiler water and when ___________ out of solution on a hot metal surface, forms a hard dense scale.
The hot lime-soda process is most suitable for the softening of _____ hardness supplies.
The hot process softener is used in conjunction with _______ filters, which are usually necessary to filter out any carryover of sludge particles from the softener.
Natural, untreated water contains dissolved mineral salts.
The sodium zeolite softener uses the principle of _________ exchange to convert scale-forming salts, in the water, into non-scale forming salts.
The softener contains a granular material called ______ , which has the ability, to remove the calcium and magnesium cations from the water and to replace them with sodium cations.
When the zeolite material has given up all its Na+ cations in exchange for the Ca2+ and Mg2+ cations, it has to be _________ before it can resume the softening process.
The regeneration is done by removing the zeolite softener from service and filling it with a solution of ______ .
The sodium hydroxide may cause _________ of the boiler metal.
A hydrogen zeolite softener is used to remove the scale forming _____ , without the formation of sodium bicarbonate.
When the resin becomes exhausted of _________ ions, it is regenerated. Sulphuric acid is passed through the resin.
The de-gasifier tower used in some external water treatment programs:
a. Removes oxygen from the make up water
b. Removes carbon dioxide from the effluent of hydrogen Zeolite unit
c. Adds oxygen to the make up water to aid deaeration
d. Is installed in the system before the softeners
e. removes carbon dioxide from the effluent of the anion unit
Removes carbon dioxide from the effluent of hydrogen Zeolite unit
Dealkalization processes reduce ________, principally carbonate and bicarbonate anions.
The _______ process, and the associated chemical reactions of a weak acid cation dealkalizer, is similar to a hydrogen zeolite softener.
The water coming out of the weak acid cation dealkalizer contains the residual (non-exchanged) hardness ions and carbon dioxide. This carbon dioxide, due to its potential to cause corrosion problems on the piping systems and downstream equipment, is degasified.
In water treatment, demineralization refers to the removal of all mineral salts, using ______ exchangers.
All demineralization systems consist of a minimum of one cation exchange process and one anion exchange process.
Strong ______ exchangers are required for silica removal.
If allowed to remain in the water, _______ acid will break down into carbon dioxide, which causes corrosion.
Each ion exchanger, in a demineralization system, must be regenerated when its _____ becomes exhausted.
The mixed bed exchanger is a mixture of strong acid cation and strong base anion _____.
Water, with a high concentration of suspended solids, is pressurized and forced through a number of membrane modules connected in parallel is called osmosis.
Reverse osmosis can achieve a __ % removal of dissolved salts, in water.
In a ______ type deaerator, the entering water passes through spray nozzles, which divide it into a fine state.
The spring-loaded valve maintains even distribution of water spray through a ____ range of flow variation.
In a _____ type deaerator, the water flow is broken up by trickling down over a series of trays.
In a _______ deaerator, steam is forced up through perforated panels as the water flows along the top surface of the panel.
In periods of low flow, steam may condense and the level will creep up. In this case, an __________ valve will open to prevent the water from rising above the level where proper deaeration can occur.
To reduce corrosion caused by oxygen, it is desirable to keep the level of dissolved oxygen in the water, at about _____ ppb (parts per billion).