1.1. Case Study: Water Pinch Analysis

1.1.1.Introduction

Water Pinch Analysis or also known as WPA is originally derived from

the concept of pinch analysis used in the chemical processes. The simple

term and understanding of water pinch analysis are reduced and reuse the

water. Nevertheless in a scientific term, WPA is a systematic methodology

to reduce water consumption and also minimizing the wastewater

generation through integration of water using activities or processes. This

analysis was first introduced by Wang and Smith. Since then, this method

has been very popular among big factory as they prefer to conserve their

water consumption, thus reducing the operation cost.

Techniques used for setting up the targets for maximum water

recovery capable of handling any type of water using operation includes the

application of mass transfer based and non mass transfer based system.

This includes the source and sink composite curve and water cascade

analysis (WCA). As a graphical tool for setting water recovery targets as

well as for design of water recovery networks, the source and sink

composite curves are used.

1.1.2.Overall Process

As shown in Figure 1, the facility uses water obtained from water

wells and water purchase from the water authority. Rainfall is also

considered as an input to the facility because it crosses the imaginary

dotted line around the facility. Figure 1 is only a rough estimation of the

water input and water output by that company.

Figure 1: Site Wide Facility Water Balance (gallons per day)

The output steams include:

a. Evaporation of water from the facility, for example cooling towers

b. Containment of the water in the facility’s products, for example a

beverage

c. Water that leaks or goes into the ground from the facility’s irrigation

system or piping.

d. Treated effluent from the facility’s on-site wastewater treatment

facility which is discharged to a surface water

e. Sanitary wastewater which are sent to an off-site wastewater

treatment facility operated by the municipality

f. After rainfall event, storm water runoff.

Facility

Well

Water

Purchased

Water

Rainfall

330,00

20,000

Evaporatio

n

Water in

Product

Water to

Ground

136,00 0 34,000

Wastewater

after

treatment to

Surface Water

Wastewater to

Off-site

Treatment

Facility

Storm

water

runoff

130,00

30,000

20,000

Sanitary UtilitiesIrrigation

Production

Purchase + well

water input

Evaporate Evaporator

30000

4000

199955

WastewaterDischarge

Sanitary Wastewaters to Offsite

Treatment Facility

30000

42874

130000

Storm water run-off20000

34000 157081

20000

Rainfall

Water in product

To ground

Water

consumed in

reaction

604545 34000

Figure 2: The plant overall water balance

Flow rate is estimated by process knowledge, engineering calculation and

or judgment, factor or a combination thereof

Flow rate is measured. For example, water meter on purchased water, flow

meter on wastewater, other measurement, e.g., the wastewater collection

tank (volume of 3000 gallons) from building A fills up and is transferred

twice per day.

Figure 2 shows an expanded view of the facility including production,

sanitary, irrigation, and utilities. Other use category where water is used

but does not fit into to one of the categories, example: quality assurance

laboratories.

- In Figure 2, notice that the well water and purchased water are

combined in one line and there is green box signifying for purposes

that the volume of purchased water and well water is measured, in

this case via water meters.

- Rainfall (in inches) is also measured via a rain gauge. By multiplying

the inches of rainfall per year by the surface area of the production

site, the volume of rainwater entering the site is estimated.

- The water outputs (other losses and wastewater discharges) from the

different areas of use are determined via inspection and process

knowledge.

- For example, the output of water used for sanitary purposes,

including water used in toilets, showers, food preparation, dish

washers and human consumption is primarily to the wastewater

collection system. For sanitary usage, there is very little evaporation

or loss to ground, except for leaks from the process waste lines or

from the sewerage system.

- Similarly, the output for water used in irrigation, for example

watering green areas in the facility, is principally to the ground via

percolation into soil or leaks from the irrigation system piping and via

evaporation. For uses in the irrigation area, there is no wastewater

discharge.

There are numerous possibilities and combinations of water inputs and

outputs. Table 1 shown on below provides common inputs and losses and

resulting discharge as wastewater.

Plant Over Balance

Common Inputs Common Losses Wastewater

Water used in production

to clean equipment,

work areas, raw

material and

product containers

If elevated

temperatures are used

for cleaning, some of

the water can be

evaporated

Most of the water that

is used for cleaning

goes to wastewater

collection system.

Water used as an input

to a water treatment

process to make higher

quality water. For

example, purchased

water is used in water

treatment process to

produce a high quality

water via distillation or

reverse osmosis

followed by a

continuous deionizer

for a pharmaceutical

production process

While classified as a

loss, the output water

from the water

treatment process is a

loss.

There are several

wastewater treatment

processes. For filtration

and carbon adsorption,

there are backwash

streams which are

discharged to

wastewater. For

softeners, there are

also backwash,

regeneration streams,

and fast and slow

rinses.

For reverse osmosis

systems, there is a

reject stream that

commonly goes to

wastewater. For

continuous water

demineralizers there

are continuous

blowdown streams. For

distillation units, there

is a blowdown stream

and water blowdown

from the condenser.

for cooling

as one pass non-

contact cooling water

Generally no losses Generally non-contact

cooling water is either

discharged to a surface

water, recharged into

the ground or sent to

an on-site or off-site

wastewater treatment

facility

to cool and lubricate

pump seals

Generally no losses Commonly this water is

discharged to the site's

wastewater system.

Water used for sanitary purposes

Toilets To wastewater

Showers To wastewater

Food Preparation To wastewater

Drinking Water Consumed though a

small amount

Dishwasher To wastewater

Area cleaning To wastewater

Water used in utilities

as an input to a water

treatment process to

produce softened water

and or higher quality

water for boiler feed

water and or cooling

tower makeup

as makeup to the

cooling towers

Water which evaporates

from the cooling tower

and drift losses from ID

fans

Cooling tower blow

down, side stream filter

blow down

as boiler feed water steam/water which is

evaporated,

water/condensate which

is lost from steam traps

Boiler blowdown

as once through cooling

for compressors,

chillers and other

equipment

Generally no losses Discharge to surface

water or wastewater

as water to inject into

gas turbines to reduce

Nox emissions

Water is evaporated Generally no

wastewater discharge

Water used for

Irrigation

to irrigate the lawns,

shrubs, plants, fields

(the green areas)

Discharge to ground Runoff can enter

wastewater collection

Calculations, Published Factors to Prepare a Balance

Sanitary Water Usage 10 -25 gallons per

person per shift

The lower value is used

where there are just

toilets. A higher value

is used where there are

toilets, showers, full

kitchen services, that

is, food preparation

and dish washing.

Irrigation Usage Number of sprinkler

heads x the flow

capacity per head, e.g.

2.5 gpm x the duration

(minutes) of water

application

Inspect the irrigation

system during

operation to determine

if there are leaks from

broken sprinkler heads

and from water

distribution lines.

Wastewater Streams from Water Treatment Operations

Reverse Osmosis Reject

Flow

Reject stream generally

ranges from 25 to 50%

of the feed to the

system

Reject flow can be

higher than the

indicated range. RO

reject streams can be

used as cooling tower

makeup if the water is

softened prior to the

reverse osmosis

system.

Backwash & Rinse

Rates

Backwash, regeneration

and rinse rates can be

obtained from

manufacturer's

literature. The rates

should be verified in the

field.

Cooling Tower Usage Sum of Water lost via

windage + water

evaporated from the

tower + blow down

from the tower

Windage is the water

driven from the tower

due the tower fans. The

windage loss decreases

if the tower is provided

with a mist eliminator.

Windage Rate Commonly 0.1 to 0.3 %

of the Recirculation

Rate

The Tower recirculation

rate can be obtained

from the manufacturers

literature and or head

versus flow curve for

the pump

Tower Evaporation Rate C x _T x Cp / (Hv) C is the tower

recirculation rate in the

units of lbs of water per

minute , T is the

temperature difference

across the cooling

tower in degrees

Fahrenheit, Cp is the

specific heat = 1

BTU/lb and Hv is the

heat of vaporization =

1,000 Btu/lb of water

evaporated

Cooling Tower Blow

down Rate

(Windage Rate x

( Cycles of

Cycles of Concentration

= conductivity or

Concentration -1) -

Tower Evaporation

Rate) / (1- Cycles of

Concentration)

chloride level in the

cooling tower

blowdown/ conductivity

or chloride level in the

cooling tower makeup

water

Boiler Usage

Boiler make up Boiler Steam Rate -

Condensate Return +

Boiler Blow Down

Boiler Blow down Range of 4 to 8 % of

boiler makeup

Table 1: Description of Common Inputs, Losses and Wastewater

Discharges

- Where the inputs and output flows are not measured, estimates of

water flow can be obtained by calculation, process knowledge and

engineering judgment.

- At many facilities, the utilities area is the largest user of water.

Reasons:

Facility in a warm climate which requires controlled humidity and

temperatures in the production and packaging areas uses a

significant amount of water in the cooling towers to remove heat

from the sites chillers

Water is blown down from the cooling tower at a higher rate than is

required to control corrosion, scaling and bio-fouling.

Facilities that generate steam for production and heating or cooling

purposes which have low rates of condensate return can use

considerable amount of water.

1.1.3.Water Consumption and Generation

The plant needs to reduce its water consumption because it was

facing uncertainty in the sustainability of its water supply for new drug

products. They rely most on the water authority for water supply.

Therefore, it is very difficult for them to get a constant water supply.

Besides, the groundwater was polluted with saltwater intrusion and also

other property contamination. Reducing consumption of water in the

factory brings a lot of impact on reliability on the water authority as well as

saving cost of production. Since pharmaceutical companies need a large

amount of water, reducing is another way to reduce cost in their plant.

Reducing wastewater generation will definitely benefits to the

environment. Water pollution has been increasing drastically throughout

the years and it have been said that the freshwater sources have been

depleting towards the years. Wastewater can be recycled, but water

treatment operations have to be used in order to recycle them. Therefore,

reducing wastewater can help the treatment plant to lessen their burden as

well as preventing pollution to the environment. As for the plant, the

wastewater generated from the utilities is less polluted and can be treated

or safe to be used for other purposes such as sanitary and also irrigation.

From here, it will not only reduce the wastewater generation but also

reduces the water consumption in the plant. This enables the company to

use the water more efficiently.

1.1.4.Water Pinch Analysis

1.1.4.1. Introduction

Water Pinch Analysis or known as WPA is a concept of systematic

technique for reducing water consumption and wastewater generation

through many processes or activities that uses water. This concept

originates from the heat pinch analysis. The WPA was first used by Wang

and Smith. From there onwards, it has been widely used as a tool for water

conservation in industrial process plants. Now, they have even applied it for

urban or domestic building.

Techniques for setting targets for maximum recovery of water

capabilities of any type of water using operation includes mass transfer and

non mass transfer based systems. These include the course and sink

composite curves and water cascade analysis (WCA). The source and sink

composite curves is a graphical tool for setting water recovery and also the

design of water recovery networks.

We have identified one of the software which is called the Water

Design. Water Design is a software tool which is sufficient for developing

many aspects of water pinch analysis and synthesis. This software could

cover chapter 1 to 7 of the Industrial Water Reuse and Wastewater

Minimization by Mann, J.G. and Y.A. Liu, Mcgraw-Hill, 1999. It originates

from the Virginia Polytechnic Institute and State University, Blacksburg,

Virginia, United States.

1.1.4.2. Advantages

Advantages

Free software

Easy to install and user friendly

Capable of solving most of the water pinch analysis problems

Compact size of software size

Won many awards from the institution level up to international level.

Compatibility with Window Vista, and XP

1.1.4.3. Important Parameters

The important parameters that have to been included into the software are

Limiting flowrate (ton/hr)

Limiting inlet concentration (ppm)

Limiting outlet concentration(ppm)

1.1.4.4. Approach used and why, source to be reuse and assumptions

As for the approach for the plant, firstly, the main water source usage was

analyzed into sections. From here, few sections have been analyzed to

have large amount of water consumption. The water consumption is as

follows:

Section Water Consumption (gallons per

day)

Production 66,045

Sanitary 30,000

Irrigation 34,000

Utilities 199,955

total 330000

Table 2 : Water consumption according to sections

After knowing the water consumption in each section, we analyzed the

limiting water concentration consumption in each section. Then,

assumption has been for setting the minimum water targets for the plant

water usage. Assumptions have been made as follows:

Section Limiting Inlet

Concentration(ppm)

Limiting Outlet

Concentration(ppm)

Production 0.00 150.00

Sanitary 5.00 100.00

Irrigation 5.00 50.00

Utilities 0.00 10.00

Table 3 : Limiting concentration for each sections

As shown above, assumptions have been made on the limiting inlet

concentration as well as the limiting outlet concentration. These

assumptions have been made from references from journals as well as

books. In pharmaceutical companies, production section must use water

with 0 ppm concentration due to consumption purposes. Most of the water

in the production section is used for cleaning the equipment and also some

are used in the process. While for sanitary, a little concentration was

allowed as the water is only used for flushing the toilet and washing the

toilet. Similarly, a little concentration was also allowed for irrigation as it is

only used for flowering and gardening purposes. Utilities must use 0 ppm

water concentration as well, due to prevention of corrosion and also

contamination of the equipments. Utilities refer more to cooling towers and

boilers in this section.

The source of stream wanted to be reused is the water from the

utilities because the wastewater does not contain too many impurities

inside it and therefore, can be used for irrigation and also sanitary

purposes.

1.1.4.5. Process flow diagram of the water analysisFigure : Process flow diagram of the water analysis

The blue line denotes freshwater, green line denotes recycle water

and finally the red line denotes wastewater. Operation 1 represents

production, operation 2 represents sanitary, operation 3 represents

irrigation and finally operation 4 represents utilities. The diagram also

denotes the impurities concentration at each operation. The limiting inlet

and outlet concentration is also shown to let the users know the amount of

water that can be recycled. As shown, operation 4 which is the utilities can

recycled back their water source to the operation 2, sanitary and operation

3, irrigation at 10ppm. This is because the water concentration recycled

back into the operation 2 and 3 is within the range acceptable for the

operation (Table 2 ). Total flow rate recycled is also shown in the diagram

with 2.35ton/hr for operation 2 and 2.70 ton/hr for operation 3.

1.1.4.6. Results of the approach and how to use pinch analysis

Our approach is quite similar with the water pinch analysis results.

From the assumption made on the limiting concentration of the water, we

can estimate the water source that we can recycle. As estimated, the water

source from the utilities can be recycled due to the low contamination of

the water. By inserting the data into the water pinch analysis, it shows that

which operation we can recycle the water from. Indirectly, this can reduce

the water consumption for the respectively operation later on. From this

case, water consumption for sanitary and also irrigation can be reduced

because the water consumption can be recycled from the water used in the

utilities.

1.1.4.7. Graphs and diagrams to support our results

There are two diagrams that can be used to support our results. As

we can see from Figure 1, water concentration at operation 4 is within the

range of operation 2 and 3. Therefore the water pinch can be applied into

this section. The water pinch can be done at 10 ppm as highlighted in the

diagram.

Figure 1: Concentration-Interval Diagram

While the second diagram will be the concentration-composite curve,

where it shows how the wastewater and also the freshwater intersect in the

graph in terms of concentration. Red line represents wastewater while blue

line represent freshwater. The graph shows that intersection of the red line

and blue line is at 10 ppm which represents the freshwater can be pinch for

usage in the operation. Each slope represents the water concentration in

the operation. The minimum flow rate is 31.20 ton/hr while the average

outlet concentration is 77.15 ppm.

Figure: Concentration-Composite Curve Graph

1.1.5.Conclusion

Before water pinch analysis, total water consumption is 330000 gpd.

After water pinch analysis, the total water consumption is 266000.

Therefore, there have been reductions of 64000gpd in the water usage or

19.4% in percentage terms.