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Energy-savers for pulp and
paper industry
Chennai, November 30, 2000
At a time where there is a dearth
of available resources and fossil fuels are fast dwindling, energy conservation
assumes gigantic importance. This applies to every sphere of economic activity.
The pulp and paper industry in India
is more than a century old, with over 140 mills as on date with a production
capacity of around 30 lakh tonnes per annum. The industry uses considerable
amount of energy in the form of steam and electricity. Electricity charges
as a percentage of the total cost of paper is more than 25 per cent. Electrical
energy has to be saved and conserved in this industry, which is plagued
by increasing operational costs and is struggling to compete amid global
competition.
The mills
can be classified into three large categories: Small mills with
a production capacity of around 10 to 30 tonnes per day; medium-sized ones
with a production capacity of around 31 to 100 tonnes per day and large
mills with a capacity of around 300 tonnes or more per day. The classification
is relevant to the Indian scenario and cannot be compared with advanced
country standards where production capacity ranges between 1,000 tonnes
and 2,000 tonnes or more per day.
What often hinders energy-saving
measures is the cost factor that often forces entrepreneurs to postpone
taking the necessary measures. Engineers are faced with the challenge to
suggest practical and viable suggestions. The measures can be broadly classified
thus: Those that give savings with no investment, those requiring a small
investment, and those with a large investment.
For small mills
These mills, by the lack of economy
of operation and size, are wasteful in their use of energy. The efficiency
of equipments in utility areas does not lend itself to good energy saving
practice. However, a few measures can be adopted to save electrical energy
to a considerable extent.
Zero investment measures:
Check the running load of major process
equipments in different sections, like raw water plant, pulping plant and
paper plant and size the motor capacity to rating as close as possible
by shuffling the motors so that efficiency is at the maximum. In some cases
a simple connection change of the motor, from delta to star, will make
the motor operate to near full load and increase efficiency, resulting
in a lower consumption of energy.
Observe discipline in the usage of lighting.
Rearrange or switch off lighting at designated times, automatically or
manually.
Avoid wasteful running of equipments
and observe discipline in processes like cutting time spent in ‘brokes’,
which not only waste energy (in cycling it back) but also lead to a loss
of valuable production time.
Observe discipline in the consumption
of water and air, thereby reducing the load on the motor and consequently
saving electrical energy.
Shut down totally or remove process
equipments like refiners that were added with no real contribution to the
process by way of quality.
Small investment
measures:
Improve power factor to 0.96 or above
to reap considerable benefits in reducing demand charges.
Change lighting system to an energy
saving type like high-pressure sodium vapour lamps.
Change equipments by making small investments
in pumps to increase efficiency.
Major investment measures:
These are not applicable to small
mills but they will be well advised to integrate measures available under
this category while expanding their unit. This however is outside the scope
of this article.
For medium sized mills
Measures with no investments are
identical to the ones listed under the small mills category.
Small investment
measures:
Install power factor improvement capacitors
to improve power factor to 0.98.
When adding equipment, install energy
efficient motors which have a flat load vs. efficiency curve from 25 to
100 per cent and whose efficiency is greater by two per cent than normal.
Monitor demand from Utility (grid supply)
and install a demand monitor to cut off non-critical loads when the demand
reaches a predetermined level to peg the demand and save on increases in
utility costs.
Major investment measures:
Replace outdated refiners and replace
these with efficient refiners like double disc type with KW transmitters.
Replace outdated vacuum pumps with new
ones with increased efficiency.
Install variable frequency drives for
all mechanical variators of speed, ID fan in Boiler House and in drives
where there is variation in speed and frequent changes of load due to speed
and valve opening in case of pumps to change the flow like stock pumps
in paper machine.
For large mills
Zero investment
measures:
The first four measures listed under
this category for small mills apply here too.
Large investment
measures:
Install variable frequency drives for
all mechanical variators of speed, ID fans in Boiler House and in drives
where there is variation in speed and frequent changes of load due to speed
and valve opening in case of pumps to change the flow like stock pumps
in paper machine.
Check the specific consumption of refiners,
paper machine vacuum pumps based on their design and check their consumption.
If the specific consumption is more it is necessary to change the equipment
matching the needs.
Replace old lighting system with energy
efficient high-pressure sodium vapour lamps and change the yard lighting
with a few well-designed mast lightings. Lighting levels to conform to
standards.
In multi-machine mills, rationalise
and integrate the stock preparation equipments to give minimum number of
refiners and install kW transmitters to optimise consumption and quality.
Phase out small, outdated and obsolete
machines with low production capacity operating with high specific consumption
of electricity, steam and water. Compensate this decrease by optimising
production in other machines by adopting suitable methods like increasing
the number of dryers to increase production.
Run the machine at rated speed corresponding
to its basis weight and achieve low specific power consumption of electrical
energy and other utilities like water and air.
Installation of basis weight and moisture
recorder will increase the savings in steam consumption and indirect savings
in energy by way of reduced losses all round.
The specific consumption of electrical
energy should not be allowed to go beyond the following figures:
Large mills with single stream of pulp
and paper: 1,300 kWh/tonne of paper.
Large mills with multiple machines with
multiple stream of pulping (old mills): 1,400 kWh/tonne.
Replace old pumps with high-energy pumps
in old mills. A considerable portion of a pulp and paper mill consists
of pumps and optimum use of these will lead to substantial savings in energy
as detailed earlier for medium sized mills.
Large mills invariably have in-plant
generation by way of steam driven turbo-generator sets with extraction-cum-condensing
turbine. Optimum use of this turbine with maximum cogeneration with minimum
condensing saves considerable energy both in steam and electricity costs,
as co-generation costs are much cheaper than utility electrical costs.
In certain cases where grid tariff is
quite high vis-a-vis co-generation power/condensing power, it is prudent
and economical to opt for in-plant generation for the whole mill and to
keep grid power to bare essentials to keep the energy costs, outage and
tripping to a minimum. Paralleling with grid will be equally effective
if the grid is stable.
The yardstick
of specific energy consumption shall be used as a tool to monitor energy
consumption. It will be interesting to note that a saving of 100 kWh/tonne
of paper on specific power consumption will translate into Rs. 5 crores
per annum in a mill with a production capacity of 100,000 tonnes per annum,
corresponding to 300 tonnes per day of production and assuming Rs. 5 per
kWh of electrical energy saved.
The above mentioned are broad measures.
Individual mills need specific approaches tailored for their needs. The
engineers and production personnel will have to work hand-in-hand to achieve
the best results, for the use of electrical energy is increasing costs
day by day. And adding costs to the final product is a sure way to lose
to competition.
The author, Scope Marketing and
Information Solutions can be contacted at scope_marketing@vsnl.com
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