HEAT RECOVERY APPLICATION IN TEXTILE INDUSTRY
Author: Arasta Dış Ticaret ve Makine Sanayi Ltd. Şti
Summary
Energy is an important part of our lives today. It is important that we use it wisely for
today and for our future. Today whole around the world, companies started to deal very
unreliable energy prices from petroleum, natural gas etc. These all have limited supply and
will eventually become depleted and increasingly more expensive, not being able to meet the
ever increasing world demand for them.
Today is the time to re-think, how to use our energy efficiently to develop a strong and
healthy companies, energy for today and tomorrow. Tomorrow companies much more rely
on efficiency to stay on market.
We also strive to make existing use of energy more efficient. Our heat recovery
systems are designed to be highly efficient in the use of your resources such as waste water
etc. Especially polluted waste water can not be re-used in any process which should be
discharged but according new EU ecological protection regulations and on top of that if we
have a biological water threatment plant , waste water outlet temperature must be cooled
down to under 30 C.
Also heat recovery systems are designed to economically recover energy that is
normally wasted. Investment pays back itself in a very short time period (Depending on seize
of heat recovery system up to 2-9 months) our industrial systems are designed to incorporate
up-to-date equipment for the most efficient operation.
For an example if we have between 25 to 175 m³/h clean water with the temperature
between 15-20ºC, heat recovery systems can heat up this clean water up to 55-60 ºC by
using nearly same amount of waste water.
After filtration process for existing fibre contents, hot waste water enters in primer side
of free flow, wide gapped plated heat exchanger, at the same time on the other side (
seconder side ) cold clean water flows as counter current in to the plated heat exchanger. In
this process clean cold water heats up and waste water cools down .
According to clients request, all process can be controlled by electro-mechanically or
PLC option. Maximum heat recovery can be obtained with the minimum expenditure. Free
flow, wide gapped plates are used in heat recovery systems. All surfaces in contact with
fluids are made of AISI 316 stainless steel.
1 Introduction
Raw oil prices has reached 70 USD per barrel in 2005, That experts predicted the fuel
oil and natural gas prices are going to be likely higher in the future.
Turkey is the one of the countries which uses high costed energy in the world. %42 of
the electricity produced in 2004 which is gained from natural gas sources. To stay on
competative course, our all industrial sectors and especially textile sector should focus on
energy effenciency matter. At the past Textile sector has faced many difficult periods and
succeed in being competative.
In spite of China, Egypt, Syria and far east countries are becoming manufacturing focal
points, Turkish Textile Sector is to reduce input costs. In an average textile dye house, main
supplies are fresh water fuel (Fuel-Oil, natural gas & LPG ), workforce , electricity and
chemical substances. With in this energy costs became first priority with the margin of %3035 percent of all costs .
Waste water and polluted waste gas are produced as an outcome of production,
Some factories solve this problem by discharging their waste to central water treatment
process , or some have their own chemical or biological water treatment complex.
2 MAIN ENERGY SAVING SOURCES IN A TEXTILE DYE-HOUSE
All well-known heat recovery methods can be applied for Textile dye houses such as
study on increasing the Boiler efficiency, usage and distribution, isolation, heat recovery
solutions from waste gas etc. of heat to minimize costs.
In order to keep the chimney gas temperature at an optimum level, a qualified steam
boiler shall be chosen in accordance with the capacity. Periodical cleaning of the smoke
pipes and elimination of the hardness of the boiler water are preliminary provisions for a
correct boiler operation. In spite of this there is energy lost by the high temperature of
chimney gas where this lost energy can be recovered by economizers to be placed in the
pattern of chimney gas. The energy that blow down water carries can be recoved by the help
of Plate Heat Exchangers. Additionally, recovery by plate heat exchangers from flash steam
capacity which the condense water has is also an application which is in use.
There is 20-30% heat recovery source in the dye-houses which its application is
unfortunately not yet widespread. Just to give an approximate value, we can say that
percentage of dyehouses that constructed this system is about 20-30%. The rest already has
information about the system but are not much interested in the investment.
2.1 HEAT RECOVERY FROM WASTE HOT WATER COMING OUT FROM DYEHOUSES
Washing, dyeing of textile products mainly requires the usage of soft clean water. This
water is heated up to 90 ºC in most of the applications and is discharged. Since this water is
dyed and polluted with chemical materials, it cannot be used directly in the process. Waste
water coming out from the dyehouse is transferred either to the facory’s own treatment
system or to the central water treatment system. The inlet temperature of the waste water
which is sent to the treatment system shall be below 30 ºC in order to have efficient
treatment. Waste water capacity is about 100 times of the daily fabric amount to be dyed.
In a factory which is planned for heat recovery from waste water, the dyeing machines
shall be provided with equipments to seperate cold and hot water discharging, and discharge
channels in the factory shall be arranged seperately for cold and hot waste waters. Feeding
of the machines shall be seperated into 2 lines for hot and cold clean water feed.
By this way, waste in the cold dirty water channel can directly be sent to treatment
plant, water in hot dirty water channel is transferred to the heat recovery system and returned
back to the treatment system after utilizing from its heat.
But most of the textile factories are not arranged accordingly. There is one outlet on
the machines and is fed through one line with cold water. Cold and hot water coming out from
the machines are discharged to together to a general channel.
It makes the heat recovery application difficult when the hot waste water is not
transferred through a seperate channel. The cold waste water which has no thermal value
increases the flowrate and reduces the average water temperature when it is mixed to waste
hot water. This results in requirement for higher capacity equipments in the design which also
increases the investment costs and electrical energy costs.
But even in this situation, the investment amortize itself within less than 1 year.
2.2 EQUIPMENTS FOR SYSTEMS OF HEAT RECOVERY FROM DYED WASTE WATER
FROM DYEHOUSES
Waste hot (dyed) water is passed through a coarse filter in order to eliminate most of
the possible dirts in it. Rotating filter, static filters or grid type filters placed in waste water
channels can be used. By this way, blocking of the pumps, plate heat exchangers and other
equipments in the system must be prevented.
Hot waste water is transferred to a balancing pool prepared according to the altitude
of the discharge channel. The hot water is transferred from an altitude close to the bottom
part of he pool to the primary section of the Plate Heat Exchnager by a centrifugal pump (1
pcs is spare). In the freeflow heat exchanger which has a multipass design, the waste water
transfers its heat to the clean water and cools itself down, then it is passed to the treatment
plant.
The plates of the plate heat exchanegr is made of AISI316 quality stainless steel so
there is no risk of rusting on the surfaces which are in contact with the water. Automatic backflushing system placed on the dirty water inlet line, sends the fibers which can enter to the
plate heat exchanger out of the system before they cause any blocking. Cold clean water
enters to the seconder section of the plate heat exchanger through related connection, is
heated with the energy from the dirty water and is transferred to the clean water storage tank.
This clean hot water is transferred first to a pressure tank by a receiver and then to the hot
water distribution line of the factory.
Figure 1: Diagram Of The System Flow and Instruments
It is possible to construct the pools, which can be seen in the diagram of system flow
and instruments, under the ground and the engine room totally under the ground and
between the pools. This possibility is a good solution for lack of space.
Depending on the water usage requirement, it is usually enough to arrange the pool
capacities about 100 – 200 m³. The pools are required to be constructed with thermal
isolation from outside and leakage isolation from inside.
The levels in the pools are controlled. When the dirty water pool is at minimum level
the dirty water pump stops automatically, cold water inlet valve is automatically closed and
when the level returns to normal pump starts to work and the valve opens. When the clean
water storage tank reaches to minimum level, the pressure tank pump stops, and returns to
working situation again when the level is normal. When the clean water storage tank reaches
to maximum level, dirty water pump stops, clean water inlet valve is automatically stopped.
The pump starts to work and the valve is opened when the level is normal again.
There are pipings and valves on the heat exchanger for back-flushing (Figure 2). The
back-flushing valves are controlled by pressure difference transmitters. When the pressure
difference is more than the set value the back-flushing period automatically starts and the
blocking in the heat exchanger is eliminated.
Same operation can also be supplied by time counter or by using pressure switch.
Pressure tank pumps are working automatically under the control of pressure switches
and level controllers and observation or inspection of workers are not required.
Construction of the system takes 2 months including the pools, and payback of the
system is about 2-8 months.
Figure 2: GEA FA 184 Free Flow Plate Heat Exchanger With Back-Flushing System
2.3 DE OF HEAT EXCHANGER
It is a must to use Plate Heat Exchanger in such systems because the the Logarithmic
Temperature Difference (LMTD), which is a very important parameter in heat exchanger
designs, is very low. The heat transfer coefficient of the plate heat exchnagers is 5-6 times
more than shell-and-tube heat exchangers which results in smaller sizes of the plate heat
exchangers when compared to shell-and-tube heat exchangers.
Choosing the correct plate type is the most important parameter in plate heat
exchanger designs. Channels on the plates and gap dimensions between the plates are very
important for waste water heat exchangers. Convensional (varitherm type) plate heat
exchangers which are designed for the supplement of high turbulances in clean water and
steam applications are blocked in a very short time by textile fibers.
Figure 3 Varitherm type Plate Pack.
Figure 4 Free Flow Plate Pack.
“FREEFLOW” plates (Figure 4 and 6) present in the product range of GEA Ecoflex
plate heat exchangers are especially designed for fiber containing, and / or viscous fluids
used in food, paper and textile industries. For example; N40 with 6mm plate gap and 0,8mm
plate thickness; FA184 with 12mm plate gap and 0,9mm plate thickness are the most
appropriate plates types for such applications.
It is also possible to increase the capacity of these plate heat exchangers within certain
limits by addition of plates. In addition, the possibility to remove the plates, supply easy
cleaning and putting back to the frame is a big operational advantage.
Another advantage of GEA Ecoflex Plate Heat Exhangers – when compared to
competitors – is that the plate gap has no narrowing points and goes along the plate with
constant diameter. Different examples can be seen below in Figure 5.
Şekil 5 :Plate Gap Cross Section of FA 161, N40 ve FA 184 Model GEA Heat Exchangers
Mixing of clean and dirty waters in the plate heat exchangers is only possible in case
the AISI 316 plates are destroyed and holes are formed on these plates. Otherwise, in case
of any problem with the gaskets the fluids are going to flow out (Figure 6) without mixing to
eachother.
Figure 5: In case there is any leakage in the gaskets, the fluids are going to flow out and are not going
to be mixed with eachother.
Figure 6: GEA Ecoflex Free Flow Plates.
3 CALCULATION OF THE ADVANTAGE FROM HEAT RECOVERY
A feasibility study is presented below.
FEASIBILITY FOR WASTE WATER HEAT RECOVERY
Parameters
Price of natural gas
Unit
YTL/Sm
Value
0,356699
kcal/Sm³
8.250
day
300
Flow
(ton/h)
Inlet
Temperature
Waste water
148,58
( C)
60,00
Clean water
151,00
3
Min thermal value of
natural gas
Annual working days of
the factory
SYSTEM DATA
Value
0,1198
90%
YTL/€
Parity
Outlet Temperature
1,65
Energy Gained (kcal/h)
o
( C)
0
18,00
Unit
YTL/kWh
Electric (Single term
industry)
Boiler yield
28,40
4.687.349
55,00
Fuel Quantity To Be Saved Within One Year and Its Monetary Value
Fuel Quantity To Be Saved Sm3
1 Hour
631
1 Day
15.151
1 Year
4.545.309
Monetary Value Of The
Savings
Euro/Day
Euro/Year
3.275
982.610
Euro/Hour
136
Operating Costs Of tHe Heat Recovery System
Annual Electical Energy Consumption Of The System
Quantity
Power KW
Consumption kWh
1
32
230.400
Pumps
Waste water pump
Total Electical Energy Cost Euro/Yıl
Maintanance Cost
16.728
2.500
EXPENDITURES
Purchase amount of investment
Annual operating cost
Annual Maintanance cost
€/YIL
Capital expenditure
Amortization expenditure
€/YIL
€/YIL
MONETARY
UNIT
€
€/YIL
2.500
COSTS
90.000
16.728
6.300
18.000
TOTAL COST OF THE INVESTMENT
EURO
133.528
SAVINGS TO BE SUPPLIED BY THE
INVESTMENT
EURO/YEAR
982.610
PAYBACK TIME OF THE INVESTMENT
Capital expenditure
6.300
Amortization
expenditure
=
=
Purchasing Cost Of The Investment * Annual Avg. % 7 Interest Rate
90.000
*
7%
=
=
18.000
Payback Time
1,6
1,6 AY
MONTH
Purchasing Cost Of The Investment
/
90.000
/
=
=
Expenditure
133.528
5
5
/
/
Income
982.610
4 RESULT
In this study, heat recovery possibilities in the textile industry and especially in
dyehouses are indicated and the level of savings supplied by the thermal energy of the dyed
waste water is evaluated.
The systems presented are already in use and achieves high success. Diffulties can
be faced at the beginning in designing the system and chosing the equipments, especially in
determining the plate heat exchanger type and capacity. Automation is required where an
automation level which does not need personal inspection of any worker is going to be
enough. Variable automation system alternatives can be supplied according to customer
requirements.
Requirement for energy recovery is known and accepted by different industries. By
heat recovery in textile industry the companies can supply high reduction in fuel consumption.
Milhan
Arasta Dış Ticaret ve Makine Sanayi Ltd. Şti