Report
to/Rapport au :
Planning and Environment Committee
Comité de l'urbanisme et de
l'environnement
and Council / et au Conseil
20 December 2006 / le 20 décembre 2006
Submitted by/Soumis par : R.G. Hewitt,
Deputy City Manager/Directeur municipal adjoint,
Public Works and Services/Services et Travaux publics
Contact
Person/Personne ressource : Kenneth J. Brothers, Director/Directeur
Utility Services/Services publics
613-580-2424 x22609, ken.brothers@ottawa.ca
SUBJECT: |
ROBERT O.
PICKARD Environmental CENTRE - ENERgY MANAGEMENT PLAN |
|
|
OBJET : |
Centre Environnemental Robert o. pickard - PLAN DE GESTION DE
L’ÉNERGIE |
REPORT RECOMMENDATION
That Planning and Environment Committee and Council receive this report for information.
RECOMMANDATION DU
RAPPORT
Que le Comité de
l'urbanisme et de l'environnement et le Conseil municipal prennent connaissance
du présent rapport.
BACKGROUND
The
purpose of this report is to communicate to Council and the public the manner
that energy consumption at the Robert O. Pickard Enviromental Centre (ROPEC) is
managed utilizing the digester gas cogeneration plant, the emergency diesel
generators and the Supervisory Control And Data Acquisition (SCADA) system to
minimize overall costs for natural gas and electricity. Over the years Process Control staff has
developed a sophisticated protocol to optimize the use of available systems to
minimize costs.
The
ROPEC wastewater treatment plant was rebuilt and expanded with the addition of
secondary treatment between 1988 and 1992.
The plant was commissioned in late 1992 and came into compliance with
the Ministry of the Environment Certificate of Approval discharge criteria
before the end of that year. The plant
was equipped with an emergency power supply consisting of three diesel
generators capable of producing 4800 kW of electrical power. This system was intended to provide
sufficient power to operate the main pumps, the digester gas system, SCADA and
all emergency systems such as lighting and fire alarms. Digester gas, consisting of methane and
carbon dioxide, produced in the anaerobic digestion process was burned in
boilers to produce hot water which, in turn, was used to heat the digesters to
the required 36 degrees Celsius and for building space heating. In cold weather, natural gas was used to
supplement. During the summer the gas
was burned in the boilers and the unneeded hot water was cooled with effluent
water to get rid of the excess heat.
A
cogeneration plant was undertaken to better utilize the digester gas in
recognition of an inefficient use of this valuable energy source. Commissioned in 1997, the plant uses three
Caterpillar 16 cylinder reciprocating engines burning digester gas to produce
about 2400 kW of electricity. The heat
from the engine cooling systems and exhaust (2800 kW of thermal energy) is
captured through heat exchangers that are, in turn, connected to the plant’s
hot water heating system. Gas produced
in excess of the requirements of the cogeneration engines is burned in the hot
water boilers or flared if the heat is not required. Natural gas is used to supplement in cold weather as needed.
The
$4.5 M investment in the cogeneration plant was returned by 2002, (net of all
related financial and maintenance costs) and today saves approximately $1.565
million dollars per year in electrical and natural gas purchases.
The
current Hydro rate structure defines a consumer with an average monthly peak
demand less than 5,000 kW as a "General User" and those greater than
5,000 kW as a “Large User”. The total
electrical power demand at ROPEC is typically about 5,300 kW; however, rain
events that increase flow to the plant can result in short term peaks of up to
8,400 kW. The total cost of electricity
contains a number of charges based on two components: the total amount of
energy consumed (kWh) and the monthly peak demand (kW) over three consecutive 5
minute periods. If ROPEC were to be
classed as a Large User the City would be subject to higher peak delivery
charges and fixed rate administration charges.
This would amount to approximately $165,000 per year. To further complicate matters, "time of
use" rates were introduced in May 2006 whereby the rate per kWh increases
during higher demand periods. The
higher rates are charged during the midday/evening in the summer months and in
the morning and late afternoon/evening during the winter. It is critical to optimize available
equipment and operating protocols to avoid the Large User designation and the
higher rate periods.
Maximizing
the availability of the cogeneration plant is essential to minimizing
electrical and natural gas purchases.
Essential maintenance work is done in low demand periods and all efforts
are expended to have the engines available during high demand periods. Net of all maintenance costs, cogeneration
saves approximately one million dollars in power consumption per year.
To
avoid the higher peaking charges of a Large User, Process Control staff closely
monitor power consumption through the SCADA system. When the purchased power approaches the 5,000 kW threshold they
will peak shave by dropping electrical loads if the anticipated peak is
expected to be of short duration or by starting the emergency diesel
generators. This saves approximately
$165,000 per year.
The
use of the hot water from the cogeneration plant for building heating reduces
the cost of natural gas purchases by approximately $400,000 per year.
With
the introduction of "time of use" rates, ROPEC staff are modifying
process operations wherever possible to take advantage of the lower rates. This work is just being undertaken and is
expected to yield significant savings.
These
measures contribute to the overall cost effectiveness of ROPEC which has one of
the lowest unit cost of any secondary treatment plant in Canada at $129.06 per
million litres treated (2005 OMBI data).
It should be noted that the OMBI Water and Wastewater Expert Panel
recently selected the Energy Management Plans for ROPEC and the Lemieux and
Britannia water purification plants as examples of best management practices to
guide other cities.
The capacity of the anaerobic digestion process is being increased by the addition of two new digesters which are currently under construction and are expected to be in operation by 2008. This increased processing capacity coupled with system growth will increase the production of digester gas. It is anticipated that the addition of a fourth cogeneration unit will be economically feasible by 2010 and funding has been identified in the Long Range Financial Plan for this purpose.
CONSULTATION
No public consultation was undertaken as this is an information report.
FINANCIAL IMPLICATIONS
The ROPEC Energy Management Plan saves the City approximately $1.565 M in electrical energy and natural gas costs per year net of operating and maintenance costs.
SUPPORTING DOCUMENTATION
None
DISPOSITION
Staff will continue to optimize the use of the cogeneration plant and emergency diesel generators to minimize energy costs.