Use of energy-saving power-electronic facilities in metallurgy
ATTENTION! POWER ELECTRONICS!
ATTENTION! POWER ELECTRONICS!
Use of energy-saving power-electronic facilities in
metallurgy
Special studies initiated within TACIS program and
conducted at ferrous metallurgical works of Ukraine proved that 40% of potential power
saving could be accomplished without significant financial inflows and notable changes in
the main manufacturing process. To lower power consuming, the following methods should be
reckoned:
- production planning;
- control over fuel combustion;
- recuperation of worked-out heat;
- broad utilization of power electronics.
Unfortunately, Ukrainian industry never gave proper heed to
utilization of power electronics despite such facilities contribute a lot to economic
effectiveness of many countries worldwide. In such countries, power transduced by
power-electronic facilities makes up 40-50% of their total power consumption, compared to
30% registered in Ukraine. As a result, power consumption of Ukrainian products exceeds
that reported by industrially developed countries 2-3 times.
Broad introduction of power-electronic facilities (formerly
called converter equipment) abroad was stipulated by a number of factors. Firstly, in most
cases the form in which electric power was generated (three-phase current, 50 Hz) made its
direct use impossible. Secondly, certain obstacles were put by existing technologies
(electrolysis, for instance). Thirdly, in some cases direct utilization of generated
electric power seemed to be quite expensive due to excessive consumption of power and
other energy resources. At the same time, when applying to power electronics any
parameters of generated power can be transformed into acceptable form according to the
customers’ wishes (i.e. current rectification, regulation of average or existing
voltage, change of current frequency, etc). Besides, a number of industries can enjoy the
benefits from use of power electronics at once. For instance, frequency and amplitude
regulation of three-phase current in hot and cold water pumps can diminish its power
consumption by 30-50% and also reduce the consumption of hot and cold water by 10% and 20%
correspondingly. What is more, in such case durability of water pumps increments two
times, expenditures covering pipeline maintenance and repairing feature distinct
curtailment, compensatory condensers can be excluded from the circuit, and operating
capacities can be decreased.
As regards metallurgy, power electronics can back both main
and auxiliary manufacturing processes. Speaking of auxiliary production, the broadest
utilization of power electronics falls on generator of alternating current, which usually
accounts for 50-55% of total power consumption. It is worth mentioning that alternating
current engines gained in popularity as well and now make up 60-70% of all engines used on
metallurgical enterprises. In such case, possible saving of power results from
comparatively low use of alternating current generators by Ukrainian industry (5-10% of
the total).
Speaking of auxiliary manufacturing processes, the
following facilities enjoyed the broadest introduction of power electronics:
- turbo-machine drives;
- conveyor transport drives;
- electrical filters;
- electromagnetic capacity compensation schemes and
line-balance converters;
- pick-and-place device drives.
As regards main manufacturing process, the most common
application of power electronics fell on the following facilities:
- arc furnace powering schemes;
- electrolytic section powering schemes;
- cathode-ray, plasma, and induction furnace powering
schemes;
- rolling mill, recoiler, and rewinder electric drives.
Some of the mentioned facilities should be reckoned more
carefully due to notable positive results achieved with the help of power electronics.
Adjustable turbo-machine drives
Being the most widespread alternating current engine in
Ukrainian industry, asynchronous short-circuit engines are broadly used (some 2/3 of the
total) to maintain the functioning of uncontrolled pump drives, compressor drives, fan and
smoke exhauster drives and other suchlike turbo-machines. In such cases, implementation of
frequency-controlled drives can save 20-60% of consumed power.
However, over the past years further dissemination of
frequency-controlled drives has been hampered by high prices for transducers. Taking into
account the average time of asynchronous short-circuit engines’ utilization (2,000 hours
per year), average power savings (up to 25%), and recoupment time for brought in
expenditures (3.5 years), economic expediency of frequency-controlled drives corresponded
to electric capacity that amounted to 1,000 kW in the 1990s and totals 50 kW nowadays (due
to cheapened transducers and expensive electric power).
Adjustable conveyor transport drives
It is well-known that conveyor transport drives on
metallurgical enterprises should have enhanced starting moment often exceeding nominal
moment. In such conditions, significant power losses result from compulsory use of
asynchronous short-circuit engines with increased sliding or phase rotor engines equipped
with additional resistors. To lower power consumption, frequency-regulated individual
drives for conveyor rollers should be used. Besides to power saving, these facilities will
ensure smooth conveyor starting, exclude compensatory condensers from the circuit and
bring to naught the utilization of unreliable and bulky contact-relay devices.
Use of power electronics in main manufacturing
process at metallurgical enterprises
Applying to thyristor rectifiers for arc furnace power
supply ranks among the brightest examples illustrating effective use of power electronics
in main manufacturing process. In the past ten years, steel smelting and non-ferrous
ferroalloy making featured broad implementation of direct current arc furnaces, which led
to the following positive implications:
- consumption of graphite electrodes dropped 3-7 times
depending on charge quality;
- specific consumption of electric power lowered by 10-80%
per ton of smelted steel;
- waste of metal (including alloying elements) decreased by
30-80%;
- lining durability witnessed distinct augmentation;
- gas and dust emission narrowed 7-10 times while noise
floor abridged from 120 dB to 85dB;
- current stabilization resulted in incremented durability
of network transformers and high-voltage switches;
- power factor rose by 30-40%.
At present, a number of European and Japanese companies
produce complex equipment for direct current arc furnaces (with capacity ranging from 0.5
to 140 tons). In particular, ABB concern launched 38 arc furnaces bearing unit capacity of
85 tons. Besides, complex thyristor rectifiers (50 kA, 800 V) are produced by
Preobrazovatel Science Research Institute and serially supplied by OJSC Preobrazovatel
(the city of Zaporozhye).
According to available data, Ukrainian enterprises are
equipped with some 300 alternating current arc furnaces with their capacity floating
within 0.5-25 tons. Should such furnaces be transformed into direct current devices, their
power consumption would drop considerably, prime cost of manufactured products would see
the same downward tendency while invested funds would be generously repaid in one year.
Estimates prove that revenues obtained from investments in
power saving measures exceed those related to increasing power generation 3-4 times. At
the same time, effectiveness of intersectoral power saving exceeds that accomplished by
separate industries 2-3 times. Thus, further use of power electronics will undoubtedly
lead to creation of more complicated and efficient power saving technologies.