Report on New Demineralized Water Plant

Submitted To: Mr. Javed Iqbal

Sr. Deputy Manager Utility Department

Submitted By: Gulfam Shahzad

Trainee Engineer Chemical

OCP TRN0702

September 2013

All natural waters contain varying amounts of suspended and dissolved matter as well as dissolved gases.  Likewise, the minerals in water suitable for drinking which are considered nutritional for the human body, cannot be handled as well by boilers. Whatever the source, impurities found in source water become an important consideration when used for steam generation.  Feedwater must be treated to remove impurities to control deposition, carryover, and corrosion in the boiler system.

Boiler feedwater is water used to supply feed a boiler to generate steam or hot water. At thermal power stations the feedwater is usually stored, pre-heated and conditioned in a feedwater tank and supplied to the boiler by a boiler feedwater pump.

The feedwater must be specially treated to avoid problems in the boiler and downstream systems. Untreated boiler feed water can cause corrosion and fouling.

Boiler corrosion

Corrosive compounds, especially O2 and CO2 must be removed, usually by use of a deaerator. Residual amounts can be removed chemically, by use of oxygen scavengers. Additionally, feed water is typically alkalized to a pH of 9.0 or higher, to reduce oxidation and to support the formation of a stable layer of magnetite on the water-side surface of the boiler, protecting the material underneath from further corrosion. This is usually done by dosing alkaline agents into the feed water, such as sodium hydroxide (caustic soda) or ammonia.

Fouling

Deposits reduce the heat transfer in the boiler, reduce the flow rate and eventually block boiler tubes. Any non-volatile salts and minerals that will remain when the feed water is evaporated must be removed, because they will become concentrated in the liquid phase and require excessive "blow-down" (draining) to prevent the formation of solid precipitates. Even worse are minerals that form scale. Therefore, the make-up water added to replace any losses of feedwater must be demineralized/deionized water, unless a purge valve is used to remove dissolved minerals.

Quality of yielding water from water demineralization plant

Hardness ～0umol/l

Silica: ≤20ug/lConductivity(25℃): ≤0.2uS/cm

The typical reactions of demineralization are as follows:

Ion exchange is a reversible chemical reaction wherein an ion (an atom or molecule that has lost or gained an electron and thus acquired an electrical charge) from solution is exchanged for a similarly charged ion attached to an immobile solid particle.

These solid ion exchange particles are either naturally occurring inorganic zeolites or synthetically produced organic resins. The synthetic organic resins are the predominant type used today because their characteristics can be tailored to specific applications. An organic ion exchange resin is composed of high- molecular-weight polyelectrolytes that can exchange their mobile ions for ions of similar charge from the surrounding medium.

The reactions of the regeneration of resin are as follows:

Common Ionic Constituents Contained in Water and Their Effects

Constituent of concern Chemical designation Resultant problemsHardness Calcium and

magnesium salts in the forms of CaCO,, Ca, Mg-

This is the primary source of scaling in heat exchange equipment, boilers, pipelinedtransfer lines, etc. Tends to form curds with soap and interferes with dyeing applications as well.

Alkalinity Bicarbonate (HCO,), carbonate (CO,), and hydrate (OH), expressed as CaCO,.

Causes foaming and carryover of solids with steam. Can cause embrittlement of boiler steel. Biocarbonate and carbonate generate CO, in steam, a source of corrosion.

Free mineral acidity H2S0,, HCl, and other acids, expressed as CaCO,.

Causes rapid corrosion and deterioration of surfaces

Chloride Cl- Interferes with silveringprocesses and increase TDS .

Sulfates (SO4)- Results in the formation of calcium sulfate scale.

Iron and manganese Fe+2 (ferrous) Fe+3 (ferric) Mn+2

Discolors water, and results in the formation of deposits in water lines, boilers and other heat exchangers. Can interfere with dying, tanning, paper manufacture and various process works.

Carbon dioxid CO2 Results in the corrosion

of water lines, 1 especially steam and 1 condensate lines

Silica SiO, Results in the formation of scale in boilers and cooling water systems. Can produce insoluble scale on turbine blades due to silica vaporization in high pressure boilers.

Technical Data of 85 t/h Demin plantMulti Media filter3 sets, Designed Press= 0.6 MPa, Capacity 45 t/h, Quartz sand 800 mm, Size 0.45-0.65 mm, Anthracite 400 mm, Size 0.8-1.2 mm

Activated carbon filter2 sets, Designed Press= 0.6 MPa, Capacity 90 t/h, Activated carbon 2000mm, Size 1.0-2.0

Filtered water tank1 set, V=100m3

Cation exchanger2 sets, Designed Press= 0.6 MPa, Operating temp= < 50 oC, Capacity 90 t/h, H=1600 mm, Size 0.315-1.25

Degasifier 2 sets, Operating temp= < 50 oC, Capacity 90 t/h, H= 2000 mm

Intermediate water tank2 sets V=5m3

Anion exchanger

2 sets, Designed Press= 0.6 MPa, Operating Pressure = 0.6 MPa, Operating temp= < 50 oC Capacity 90 t/h, H= 2500 mm, Size 0.315-1.25

Mixed bed 2 sets, Designed Press= 0.6 MPa, Operating temp= < 50 oC, Capacity 90 t/h,

H=500mm, MB cation , Size 0.71-1.25, MB anion＝1000mm, Size 0.40-0.90

Raw Water Analysis at inlet of Demin Plant

Analyzed For Raw Water( After Sand Filter)PH 8.1Conductivity 220 μs/cmTDS 133 ppmTurbidity 20~40 NTUSilica 40 ppm

Multi-media filter 3 sets of filters (2 on duty, 1 standby) treatment capacity 45m3/h

The designed operation time of the system is 24-48 hours. After then, conduct backwashing on multi-media filters; adjust backwashing cycle, according to season, change of water quality, differential pressure of operation and etc, to ensure the turbidity of yielding water is smaller than 4.When the differential pressure of inlet and outlet of multi-media filters reach 0.05 Mpa, backwashing shall be conducted.Order washing (this filter needs to go through order washing when it is just put into operation or has not been used for a time before put into operation again)

Open order washing discharge valve Open inlet valve. When the turbidity of yielding water is smaller than 4, the order washing is passed. Open outlet valve. Close order washing discharge valve Start to produce water.

Backwashing

The purpose of backwashing is to make quartz sand and anthracitic coal loosen in reverse direction and wash away the impurities intercepted at filter layer as to realize the function of filter layer cleaning.When the filter operates to differential pressure of inlet and outlet≥0.05Mpa, stop producing water and start backwashing. Backwashing is conducted according to the following steps.

Close inlet valve and outlet valve Open exhaust valve. Open order washing discharge valve, observe through filter sight glass and

discharge water to 15-20cm or so at filter layer level. Close order washing discharge valve.

Rinse by air 0.2MPa Pressure at the outlet of air storage tank is 0.2MPa

Open air intake valve. Rinse by air for 2-3 minutes. Close air intake valve

Backwashing Use the water in water production tank for backwashing

Start backwashing pump Meanwhile, open backwashing inlet valve, backwashing discharge valve

and conduct backwashing for 15-30 minutes, or until discharged water from backwashing is clear. Stop backwashing pump Close backwashing inlet valve. Close backwashing outlet valve.

Oder washing Open inlet valve and down-discharge valve. When the turbidity of yielding water is smaller than 4, order washing is

passed. Close down-discharge valve, open outlet valve and equipments are in

operation condition.

Activated carbon filter2 sets of filters (1 on duty, 1 standby) (capacity 90m3/h)

The term activation refers to the development of the adsorption properties of carbon. Adsorption is the process by which liquid or gaseous molecules are concentrated on a solid surface, in this case activated carbon. This is different from absorption, where molecules are taken up by a liquid or gas. Activated carbon can made from many substances containing a high carbon content such as coal, wood and coconut shells. The raw material has a very large influence on the characteristics and performance activated carbon.

Order washingthis filter needs to be washed when it is just put into operation or has not been used for a time before put into operation again.

Open order washing discharge valve. Open inlet valve. When the turbidity of yielding water is smaller than 4, the order washing is passed.

Water production (operation)

Open outlet valve Close washing discharge valve Start to produce water.

When the filter operates to differential pressure of inlet and outlet≥0.05Mpa, stop producing water and start backwashing.

Backwashing

Close inlet valve and outlet valve. Open exhaust valve. Open order washing discharge valve, observe through filter sight glass and

discharge water to 15-20cm or so at filter layer level.

Close order washing discharge valve. Use the water in water production tank for backwashing Start backwashing pump open backwashing inlet valve, backwashing outlet valve, and conduct

backwashing for 15-30 minutes Stop backwashing pump. Close backwashing inlet valve. Close backwashing outlet valve.

Order washing

Open inlet valve and down-discharge valve. When the turbidity of yielding water is smaller than 4, the order washing is

passed. Close down-discharge valve, open outlet valve and equipments are in

operation condition.

The designed operation time of the system is 24-48 hours. After then, conduct 20 backwashing on active carbon filter; adjust backwashing cycle, according to season, change of water quality, differential pressure of operation and etc, to ensure the turbidity of yielding water is smaller than 4.When differential pressure of inlet and outlet of active carbon filter reaches 0.05 Mpa, backwashing shall be conducted.

Cation and anion beds

Order washing Open order washing discharge valve. Open inlet valve. When yielding water meets the standard, the order washing is passed.

Water production Open outlet valve. Close order washing discharge valve Start to produce water

Regeneration

When the water produced by equipment is not qualified, stop operation and regenerate. The regeneration shall be conducted according to the following steps.

Open exhaust valve, intermediate discharge valve and discharge the top water cushion layer of equipment from intermediate discharge pipe.

Add regenerative liquid Close exhaust valve. Open regenerative liquid valve, intermediate discharge valve, start

regenerative system and add acid or alkali liquid at the flow rate of 5m/h to anion and cation exchanger.

The contact time of regenerative liquid with resin is controlled at 45-60 minutes. Concentration of regenerative liquid: 3-5% hydrochloric acid regenerative cation resin 2-4% sodium hydroxide regenerative anion resin

Replacement

Close regenerative liquid valve, open backwashing inlet valve, intermediate discharge valve and enter rinse water at the flow rate of 5-8m/h When yielding water pH of cation bed =3-4, close backwashing inlet valve, intermediate discharge valve and stop replacement. Using water production of cation bed to replace anion bed, when yielding water PH of anion bed =9, close backwashing inlet valve, intermediate discharge valve and stop replacement.Open top inlet valve and bottom discharge valve. Wash resin layer at the flow rate of 20-30m/h. When yielding water hardness of cation bed≈0mmol/L and

Na+＜100ug/L, order washing of cation bed is passed

Carbon remover (Degasification) Degasification systems remove both naturally occurring gases and gases that are byproducts of various stages of water treatment, reducing the load on your ion exchange systems. Using these simple and cost-effective systems can dramatically reduce the frequency of resin regeneration cycles. And they are virtually maintenance free.

Forced Draft Decarbonators consist of an atmospheric tank filled with plastic packing on top of a clearwell. Process water is sprayed from the top onto the packing, thinly spreading the water and releasing trapped carbon dioxide. The released gas is then blown out a vent in the top of the tank by a low pressure fan, and the process water flows down into a clearwell at the bottom of the unit and out to the next stage of treatment.Used to reduce carbon dioxide content of the effluent from hydrogen cation exchangers. Reduces CO2 to approximately 5–10 ppm but saturates water with air. Also referred to as a decarbonator.Before cation bed produces water, open inlet valve of carbon remover. Fans are in one-to-one correspondence to outlet valves of cation beds, i.e., carbon remover fan being started simultaneously while at water production of cation bed.

Mixes BedMixed bed exchanger needs to go through order washing if it has not been used for a time before put into operation again or is put into operation for the first time

Open order washing discharge valve Open inlet valve When yielding water meet the standard, order washing is passed

Water production Open outlet valve. Close order washing discharge valve. Start to produce water

Regeneration of mixed bed exchanger

Alkali feedingAlkali feeding loses effectiveness Open alkali feeding valve and order discharge valve and charge 4% alkali liquid. The time any alkali liquid discharges from order discharge outlet, close alkali feeding valve to make resin completely lose effectiveness. Backwashing layering

After mixed bed loses effectiveness, it is possible to use the difference in their ratios to separate anion and cation resins by backwashing. Open backwashing inlet valve and backwashing discharge valve, adjust incoming water flow step by step to make resin obtain the greatest backwashing expansion height, conduct backwashing for 15-30 minutes and stop backwashing when anion and cation resin are layering obviously. Release water on standing Open air valve and order washing discharge valve and make resin release water to the bottom of middle peep hole, Close air valve and order washing discharge valve Ejection Fully open acid and alkali inlet valve of mixed bed, slightly open intermediate discharge valve, open acid and alkali ejector inlet valve of mixed bed Start self-used regenerative water pump, open pump exit valve, adjust acid and alkali ejector of mixed bed, maintain proper flow and adjust intermediate discharge valve to make flow and water level keep stable. Feed acid and alkali Simultaneously, feed acid and alkali, open outlet valve of acid and alkali metering tank and adjust valve openness to make the concentrations of acid and alkali 3% and 4% respectively. After acid and alkali charging is completed, close outlet valve of acid and alkali metering tank. Replacement Keep the open status of the above valves and maintain original flow of ejector, feed water on the top and bottom simultaneously, eject waste liquid out of intermediate discharge valve. The test shows that the water PH from intermediate discharge>3.7 and it is replacement destination. Open water inlet of mixed bed, open order washing discharge valve, feed water from the top and discharge water from the bottom, and conduct order washing in big flow. Until there is no methyl orange acidity in yielding water and conductivity<10us/cm, stop order washing and close inlet valve and discharge valve of mixed bed.

Release water Open air valve and close inlet valve, release water to 200mm above upper layer of resin and close order washing discharge valve. open air intake valve of mixed bed

and blow to mixture for 5 minutes by compressed air to make anion and cation resins mixed evenly. After resins are mixed, rapidly close inlet valve and bottom discharge valve to make resins drop rapidly and eliminate another layering.Open inlet valve and order discharge valve of mixed bed exchanger, start intermediate water pump according to requirements, control flow in normal condition, i.e., 85m3/hr When conductivity falls to 0.2цs/cm, open outlet valve and close order discharge valve.