Business: Industrial

Getting Ideas for Energy Management Opportunities
2.2 Utilities management

2.2.1
Managing electricity

The effort to save electricity at a foundry could
start with examining the components of its electricity bill. Often these are
not fully understood and, consequently, advantages of available savings are
not utilized. A foundry can
lever this knowledge profitably in managing electricity use on site and in negotiating
with energy companies in the new, deregulated electricity market in Canada.

The
electricity bill may have four components:

1. Consumption charge
– the
kWh consumed in a given period multiplied by the set rate, in ¢/kWh. A
second consumption charge may apply in time-of-use and seasonal rates situations.

These pricing schemes offer lower rates to customers

who can shift high-demand operations away from the periods when the utility receives
its peak demand for energy.
The utility benefits from a more consistent daily
load pattern, and the customer pays less.

The means to save:

• Reduce the total electricity consumption (in kWh)

  in the facility; and

• Shift energy consumption to a time when energy costs are lower.

2.
Demand
charge – the maximum power level used by the foundry, in kW or kVA, is
also called peak demand. The demand varies throughout the day depending on
what electric equipment is running concurrently. The electric company typically
measures the demand in 15-minute intervals. The maximum demand recorded in
the month sets the demand rate (up to $20 or more per kW) to be applied to the electricity
bill for the entire month. The electricity utility thus finances its investment
in supplying the required power to the foundry. If the foundry has its own
transformer, it may negotiate a discount.

Some billing practices obscure the
penalties involved. For example, if the demand charge combines the monthly
demand with a percentage of maximum monthly
demand
in the past 12 months, then a foundry is penalized when no production takes
place (holidays or poor business).

The means to save:

• Reduce peak demand by:
  • Load-shedding – i.e., switching off non-essential
    electrical equipment;
  • Load-shifting – i.e., rescheduling operations so
    that some activities take place during off-peak periods;
  • Process improvements,
    which reduce electrical power requirements; and
  • Negotiating, if the utility
    allows it, for a 60-minute demand- setting period, instead of the 15-minute
    period.
• Control demand with demand controllers – devices that reduce potential
  peaks and make a foundry’s operations add load to the low spots. If
  you already have a demand controller, examine its function relative to a
  frequency
  of load factor peaks. Demand can also be controlled in multi-furnace operations
  by staggering operations and using new-generation power packs, which can
  split the power between the furnaces to control the demand effectively.

3.
Power factor charge

– a penalty that the electric company
charges to customers for poor utilization of the power supplied; it is a measure
of efficiency. It is expressed as a ratio of the power passing through a circuit
(apparently supplied, in kVA), to actual power used (work performed, in
kW). Utilities penalize customers with a power factor less than a set level,
usually

90%. Deregulation will likely increase this and other penalties. Sometimes,
kVA is used in the capacity charge. This is a charge intended as payment for
the costs of supplying the service to the site, and represents
the maximum
demand from the supply system.

The means to save:

Power factor may be improved by:

• Controlling items that generate inductive
  loads, such as transformers, lighting ballasts, electric induction motors
  (especially under-loaded ones), etc.; and
• Installing capacitors in the electric system.
  The thing
  
  to watch for is that harmonics from electric furnace AC-DC-AC
  converters may trip or destroy the protection.

4.
Inducements – e.g., offering different
rates for blocks of consumption based on demand (e.g., 9¢/kWh for the
first 100 000 kWh 3 demand, 6¢/kWh
for the next block, etc.). This may penalize single-shift operations
and those with a poor load factor. Load factor is the monthly consumption divided
by the
product of maximum demand and the billing-period hours.

At other times,
utilities may offer better rates for off-peak hours in an effort to encourage
a foundry to switch to melting at night, for example.

The means to save:

• Examine your electricity bill and try to renegotiate; and
• Examine the economics
  of a different production schedule.

Most industrial and commercial facilities
are billed for electricity according to a general-service rate schedule in
which the customer pays for the peak power demand (kW/kVA) and energy consumption
(kWh). Most general-service
rate structures
also impose financial penalties on plants that have a low power factor.

Some
utilities now offer their major customers real-time pricing, a scheme in which,
each day, the utility gives the customer the rates
proposed
for each hour
of the following day.

A large foundry in Ontario joined a real-time
pricing program. Each afternoon, the foundry gets the price of kWh for the
next day, starting
at midnight.
The operators enter the price into the system and then consider the
quantities of iron in holding furnaces against the production schedule
to decide
on hour-by-hour
usage targets. Since the power is (in this jurisdiction) at its most
expensive between 10 a.m. and 11 a.m. and between 7 p.m. and 8 p.m.
every day, they
schedule melting to suit, e.g., shifting it to night melting, with
corresponding reduction
during the daytime.

Software is available for estimating energy costs
in a variety of situations to help you arrive at the best mode of use, depending
on operational
restraints imposed by factors such as equipment requirements. To
find out more about
available software and analysis tools, consult your electrical utility.
(Also see “EMOs” below.)

Consider using one of the predictive, “smart” demand
side management (DSM) programs, which are available on the market.
DSM refers to installing efficiency
devices to lower or manage the peak electric load or demand. (Note:
DSM programs are also available for natural gas usage, for example.)
A network of on-line
electrical metering enables real-time data to be collected from the
meters and allows the computerized energy management system to predict
and control the electrical
demand. When the demand approaches preset targets, non-essential
operations are cut off and held back so as to shave the peak demand.

In
conserving electricity, focus on where the potential savings are! Table 3 illustrates
where foundries use electricity.

TABLE 3:

Where foundries use electricity

In a large Ontario foundry, the monitoring of electric
energy losses within the foundry is now a way of life. Parameters such as kW,
kvar, kVA, PF (power factor), MWh, frequency, demand variations and total harmonic
distortion are monitored on a shift basis. The ECAM^® system used has a
troubleshooting capability.

Electric motors

The efficiency of older electric motors is generally much lower (as
is the power factor) than that of the new generation of high-efficiency
motors. These motors
have efficiencies above 93% (in dependence on the motor horsepower:
the higher, the better efficiency). The summary replacement of running
old motors with the high-efficiency models is often difficult to
justify unless they
run close to 24 hours a day and the power cost savings provide a
good return on
the investment. When the motors need to be replaced or sent for rewinding,
HE motors
should be purchased instead. (Provide cost justification based on
marginal motor cost difference, when the time comes for rewinding
or replacement
of the old
motor.) This should be encoded in a purchasing policy.

Oversized or
idling motors waste electricity and cause poor power factors. That is frequently
the case in motors operating sand mullers, baghouses and air compressors – usually
the biggest in the foundry. These motors, among the hardest working,
are especially susceptible to burnouts by electric induction or arc furnace
harmonics.

Other EMOs
Housekeeping

• Involve all employees – the electricity conservation effort
  must be broad-based and have the support of the operators. An awareness
  campaign should occur at
  the start.
• Review the scheduling of foundry operations in view of
  the factors involved in the cost of electricity they consume.
• Establish a baseline
  of power consumption during plant shutdowns on Labour Day, Thanksgiving
  Day, etc., for energy use tracking.
• Track and trend power consumption based on production
  and non-production days to spot the energy wasters. Then develop procedures
  and shutdown checklists to ensure that equipment shutdowns are taking place.
• Consider
  requesting help from your local utility or from NRCan’s CANMET.
  Computer-modeling programs are available that show how furnace
  operating parameters affect operating costs.
• Verify that motors are correctly sized for
  the job.
• Switch off motors and equipment when not needed.
• Install automatic controls
  for shutting down equipment when not needed.
• Review motor burnout history and
  whether circuitries in the foundry need to be upgraded.
• Use your electric utility
  as a resource: it can make suggestions as to demand reduction alternatives,
  offer points for metering and the way to
  measure consumption, and possibly lend a load analyser.
• Maintain and calibrate
  automatic controls on all equipment.
• Schedule powering of electric induction
  furnaces in sequence so as to avoid creating power demand peaks unnecessarily.
• Control
  harmonic distortion passively and upstream; specify it in new equipment
  buying standards.

Low cost

• Replace, as a matter of purchasing policy, old worn-out electric motors
  with new high-efficiency motors.
• Install variable speed drives and soft-start
  options on electric motors.
• Consider installing power load-shedding software
  in the electric induction furnaces. The software serves as an electricity
  and process management tool.
• It monitors power usage instantaneously and adjusts
  to a set target for maximum level of power it can use. It governs the consumption
  through
  a programmable logic controller (PLC). It can express real and predicted
  usage
  of
  power in kWh/t of melted iron, in kWh/t of finished product, and
  also in terms
  of costs;
  e.g., PowerPlusReporter^® software; environmental
  and energy management
  programs from E2MS Inc.
• Consider conducting thermographic inspections
  of furnaces, ovens and ladles for heat loss, and for detection
  of electrical hot spots, e.g., in
  couplings and contacts, which indicate mechanical sources of loss.

Retrofit; high
cost

• Control furnace harmonics that can interfere with and cause burnouts of motors.
• Consider
  replacing power capacitors with microprocessor-based LRC tuning circuits,
  sized for each specific equipment and power load, to control
  the power factor for improved savings. In an Ontario foundry, power factors
  close to unity, i.e., 0.98–0.99, are routine!
• When installing an energy
  management system, choose one with both analytical and reporting capability.
• Consider
  installing a power monitoring system with monitoring and targeting methodology
  to manage electricity consumption in the entire foundry.

A full
one third of the foundries surveyed in 2000 had power quality problems from
induction and electric arc furnaces,
particularly when combined with
older power supply systems. The harmonics generated caused
damage to capacitors installed
to control the power factor, tripped fuses, burned motors
and overheated
equipment. It is essential to control harmonics.

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