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Electrolytic process, used to manufacture caustic soda,
chlorine and extraction of aluminium and zinc is highly
energy-intensive. Load management, which changes the shape
of the electric load curve, so that generation by costly
peaking units or capacity addition are avoided or deferred,
is an effective technique to meet peak demand deficit. In
view of the increasing electricity prices and introduction
of time of use tariffs by utilities, electrolytic process
industries can reschedule their operations to reduce the
electricity charges. This paper presents an optimization
model and formulation for peak demand management for electrolytic
process industries. The formulation utilizes non-linear
programming technique for minimizing the electricity cost
by rescheduling the loads. The case study of a caustic-chlorine
plant shows that significant reduction in peak demand (about
17%) and electricity cost (about 9%) is possible.
Electricity has become an integral part of human life,
and it is essential for modern living and business. Electrical
energy today constitutes about 37% of the total annual energy
consumption on a worldwide basis Khatib (2003). Due to escalating
costs of fossil fuels and capital cost for building new
generation capacity, the cost of electricity has been increasing
for the last three decades. Demand for electricity is now
growing globally at a rate higher than that of economic
growth. In many developing countries, the electricity supply
industry is unable to keep pace with the increasing demands,
causing energy shortage and peak demand deficits. With the
present installed capacity of about 128, 500 MW, the Indian
power system is facing an energy shortage of 9% with peak
demand deficit of about 14% (Ministry of Power, GOI, 2007).
Electrolytic process is employed for manufacturing basic
chemicals like caustic soda and chlorine and extraction
of aluminium and zinc. Caustic soda (sodium hydroxide) is
manufactured by the electrolysis of salt brine, using mainly
by membrane cell technology. The electricity cost accounts
for almost 50%-65% of the total production cost. The total
power consumption per ton of caustic soda for membrane cell
process is around 2,850 kWh/ton (TERI, 2006). Aluminium
metal is produced by an electrolytic smelting process in
which a high dc current is passed through a bath of alumina
dissolved in cryolite. The electricity cost forms about
40% of the total production cost. In India, the industry
average for the electricity consumption in smelters is 14,000-17,000
kWh/ton of the metal produced.
Load Management (LM) programs focus on reducing the customer
use at the time of high utility system loads. Load management
has emerged as an effective technique to handle the peak
demand problem faced by the utilities. Application of LM
in industrial sector has been limited mainly due to lack
of knowledge about controllability of loads, resistance
to change from the experienced usage pattern, and variation
in demand pattern of different industrial loads.
Industrial Load Management (ILM) applications have been
reported for utilities using interruptible load control
schemes (Chen and Leu, 1990). Many utilities have already
implemented the Time Of Use (TOU) tariff rates as viable
load management option to manage their peak demand deficit.
Since the industries are bulk consumers of electricity,
the impact of LM action, like load scheduling under TOU
tariff on peak demand reduction is high.
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