Reportm4 Edited

Redesign of the chilled water circulation system in ATL project 2005-06’

7.3 ROOT CAUSES

7.3.1 WATER FLOW RATE .

The total water flow rate required for the RF unit and different mills are

maintained by using two pumps of capacity 70m3 /hr each at 70m head.

From the flow rate calculation we get the flow rate requirement for a single mill

is 0.875 lit/sec or 3.15 m3 /hr.

In the existing system the cooling rate of the mill is not uniform and

sometimes, during peak loads the temperature of chilling water exceeds the

limiting value and it may cause breakdown of the system, resulting in loss of

production.

The flow rate of water in the condenser of one RFunit is 13.6 m3 /hr

and for the efficient working the flow rate must be maintained at the standard

value.

In order to meet the peak load requirement of chilled water, the flow

rate of water in the condenser may vary and it may lead to the uneven cooling

of the system of the use of common pumps for the circulation of water to both

RF unit and mills.

7.3.2 Heat carrying capacity

In the existing system heat load distribution is non uniform, and at

times the chilled water temperature exceeds the limiting value and often

causes temporary breakdown of mills.

Dept. of ME MESCE Kuttipuram37


Major causes In existing system the RF units directly supply the chilled water to

various mills to meet the requirement. At peak load condition the RF

unit cannot supply required chilled water at sufficient flow rate.

In the existing system the there is only one chamber ,

The existing chamber is used only for the recirculation of hot water to

RFunit.

The bypass arrangement causes wastage of heat in the chamber.

7.3.3 Power Consumption

The areas of power consumption are,

RF UNIT (2X60TR +120TR)

CHILLING WATER PUMP

CONDENSER PUMPS

COOLING TOWER FAN

In this system the 3 RF units are working round the clock for supplying chilled

water. Hence the power consumption is very high.



7.4 IDEAS

7.4.1 Water Flow Rate

Water flow rate can be controlled by modifying the pumping system. we

can use separate pumping system for the circulation of chilling water to

RFunit and various machines.

7.4.2 Heat carrying capacity.

In this we separate the existing water collection chamber into two separate

wells. That is,

HOT WELL

COLD WELL

7.4.3 Power ConsumptionIn this system we are use only one 60TR and one 120 TR units

at a time to meet the average load. One 60 TR unit is used as stand by unit.

By switching off one RF unit we can save energy.



7.5 COUNTER MEASURES

7.5.1 Proposed system

In the proposed system we separate the collection chamber into

hot well and cold well and separate pumps are installed for regulating the

required flow rate to the system.

The chilled water directly comes from the RF unit to the cold well. From

there the chilled water is supplied to the various machines with the aid of

pumps. The returned water from the various machines collected into the hot

well and from the hot well the water is pumped to the RF unit and completes

the circulation.

In the proposed system instead of three pumps of 40hp, we make use

of 6 pumps of capacity 20hp each. Of the 6 pumps, 3 pumps are used for the

circulation of chilled water to various machines and the other 3 pumps used to

return the hot water to the RF unit.

The advantage of using 6 pumps instead of 3 pumps is that, a steady

flow rate can be maintained while the electrical consumption remains the

same.

7.5.2 Chilled water system with hot and cold well

These types of system have two independent of chilled water circuits

with separate pumps. One to circulate a steady rate of water flow through the

chiller known as the primary pump and second known as the secondary pump

for the process circuit.

The circuits are linked through a tank which has two compartments, one

receiving the chilled water from the chiller and the second receiving the warm

water from the process. The primary pump circulates water from the warm

compartment of the tank through the chiller and then to the cold compartment.



The secondary pump circulates the chilled water from the cold compartment

to the process equipment and back to the warm compartment of the tank.

Thus a continuous and steady flow rate of water through the chiller is assured.

To make up for the loss of water through glands of pumps and valves, a make

up line with a float level control is connected to the warm compartment of the

tank.

1. Refrigeration unit

2. Pump

3. Make up water tank



4. 3- way valve



7.5.3 Water Flow Rate.

In this system we partition the collection chamber into hot and cold

wells. We use separate pumps for the hot and cold well.

That is 70 m3 /hr, 35m head, 20HP, two pumps for circulating the chilled water

and same standard two pumps for the hot water circulation to the RF unit.

In the new system we can maintain uniform flow rate in the

different mills without considering the flow rate of RFunit.

Also we can meet the different load requirement in different mills by adjusting

the valve at the delivery side of the cold well.

7.5.4 Heat Carrying Capacity

In this we separate the existing water collection chamber into two separate

wells. That is,

HOT WELL

COLD WELL

Also we modify the pumping system, separate pumps for two wells.

Two 20HPpumps for the hot water circulation to RF unit.

Two 20HPpumps for the chilled water circulation to various mills.

In the new system chilled water from the RF unit is directly supplied to the

cold well. From the cold well, the chilled water is pumped to the various mills.

This system controls the temperature of the chilled water within the limits.

The different load conditions can easily be met by this system. Because the

cold well has sufficient quantity of chilled water at all times the supply of



chilled water within the temperature limits can be met with ease.

7.5.5 Power consumptionRF UNITS

In this system we are use only one 60TR and one 120 TR units at a time to

meet the average load. One 60 TR unit is used as stand by unit. By switching

off one RF unit we can save energy.

When the system is working it takes power in the rate of 1amps for 1TR.

The Idle Losses for the 60 TR Unit =30amps

CONDENSER PUMP

In proposed system we can switch off one condenser pump for the cooling

tower and save energy.



7.6 RESULTS

7.6.1Energy Balance

Energy balance is done by comparing the existing and proposed

system.

We analyze the heat capacity of the existing chilled water system and

the total requirements of the different mills. During peak load Losses are also

considered for the calculation.

Existing system

For one roller energy requirement is =29.33kw

For 30 rollers =29.33*30

=880kw

Available capacity ( rated ) =845kw

Losses =85kw

Net available energy capacity =760kw

From the above analysis we can infer that this system cannot meet the

requirement during peak load.

Proposed system

Out of 25 readings taken in 8 hrs, only 4 readings are higher than 240 TR

that is the (capacity of RF unit ) (16%).

With the existing system chilled water temperature cannot be maintained at

the below specified level during this peak load time.

With proposed system, as the chilled water temperature in the sump is

reduced well below during the off load time and hence the peak load can be

met with this very low temperature chilled water.



7.6.2 WATER FLOW RATE.

CALCULATIONS

Total no of mills = 15

Total no of rollers =15*2

=30

Flow rate requirement for

one roller =0.875lit/sec

Required flow rate

for 30 rollers =0.875*30 lit/hr

=0.875*30*3600

=94.5 m3 /hr

The capacity we have =2*70

=140 m3 /hr

From the above calculation it is clear that the required flow rate is easilymaintained in the proposed system.

7.6.3 HEAT CARRYING CAPACITY

The different load conditions can easily be met by this system. Because the

cold well has sufficient quantity of chilled water at all times the supply of

chilled water within the temperature limits can be met with ease.

From load conditions,

The average load of the plant is =150TR

Total plant capacity is =240TR



By using this system one 60TR unit can be used as stand by unit.

Because 180TR is sufficient for meeting the average load.

7.6.4 Power Consumption

The Idle Losses for the 60 TR Unit =30amps

The Power =√3VI COSø

=1.732*440*30*0.9

=20KW/HR

That Is For One Shift =20*10 = 200kW.

200kw energy can be saved by using this system.

CHILLED WATER PUMP

The total pump rating remains the same after modifying the system.

In existing system, power consumption = 30*40

=120hp

In proposed system =60*20

=120hp

That is the power consumption is same as before.

CONDENSER PUMP

In proposed system we can switch off one condenser pump for the cooling

tower and save energy.



Chapter-8

Cost benefit analysis

The key steps involved in determining whether a project is worthwhile or not

are,

Estimates the cost and benefits of the projects

Assess the riskiness of the project.

Calculate the cost of capital.

Compute the criterion of merit and judge whether the project is good or

bad.

There are several criteria that have been suggested by economist to judge the

worthwhile ness of capital projects. Some are general and applicable to wide

range of investments.

The important criteria are,

Net present value.

Internal rate of return.

Pay back period.

8.1 PAY BACK PERIOD

The payback period is the length of time required to recover the initial cash

outlay on the project. According to the payback criterion, the shorter the pay

back period the more desirable the project. The firms using this criterion

generally specified the maximum acceptable pay back period.



8.2 Cost analysis.In this analysis we are analyzing the financial benefits, get from the proposed

system and the various costs incurred for the modification.

The major costs we have to meet are the cost of pump. Total six pumps are

required for the modification. Out of this, three are available in the factory.

Savings

Energy saving =20kW/hr

For one year =12*20*352

=84480kwCost of one unit of

Electricity

=Rs3.5

For one year saving =Rs 295680/-

CostsCost of one 20hp;

35m head pump =1 lakh

For 3 pumps =3 lakh

Installation and miscellaneous =1 lakh

Total cost =4 lakh



8.3 Pay Back Period Calculation

Total Cost =4 lakh

One month saving =24640

Pay back period =400000/24640=16.2 months



Conclusion

In our project we are redesigning the chilling water circulation system for

obtaining maximum efficiency with minimum utilization of energy

From the analysis we can conclude that the design is cost effective and

efficient.



Reference:

REFRIGERATION AND

AIR CONDITIONING … … C P ARORA

REFRIGERATION ANANTHA NARAYANAN

WWW.bee-india.nice.in

www.em.ea.org


http://www.em.ea.org/

http://WWW.bee-india.nice.in/

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