Volume 20, number 1, June 2006

Room for efficiency and savings at the Chicoutimi Heating Plant!

Nine institutional and religious buildings located in the heart of Chicoutimi are steam heated by a common thermal power plant, known as the Centrale de chauffage de Chicoutimi. Since 2004, the power plant’s managers have been modernizing the installations with the aim of improving energy efficiency. Four energy efficiency measures have been implemented, generating annual savings of nearly 10%, or 26,530 GJ per year:

  • The first measure was the installation of a combustion heat recovery system, an indirect energy saver installed on the common smoke pipe of the four boilers leading to the chimney. This recovery system is used to preheat the boiler feedwater coming from the degasser. The degasser water, steam heated at 5 lb/in2, has a tem­perature of 227° F. This water passes into the recovery system and is reheated to 247° F. On the smoke side, the recovery system temperature is 400° F at the inlet and 280° F at the outlet. The recovery system’s capacity is 325 kW when the boilers operate at 55,000 lb/h.
  • The second measure was the installation of an automatic purge system on the boiler room’s four boilers to control the minerals in the water of each boiler. A sensor was installed in the surface water to transmit a signal to a conductivity controller. Based on this signal, the boiler controller modulates the automatic purge valve to continu­ously discharge part of the surface water and the minerals it contains.

A system was also installed to recover the energy in the purge water. A water/water plate exchanger allows this energy to be transferred to new water from the aqueduct, required as makeup water for the power plant.

The automatic purge system and energy recovery thus offer several advantages:

  • reduced volume of boiler water to be discharged;
  • water treatment and energy savings.
  • The third measure implemented was the addition of oxygen analyzers and programmable boiler regulators. First, an oxygen sensor was installed in the smoke pipe of each boiler. This type of control increases the boiler’s efficiency over the entire operating range by reducing the excess air required for combustion. The oxygen sensor sends a signal to the boiler regulator, which modulates the air intake register on the burner. The natural gas valve and the air register receive independent commands, thus increasing the precision of the controls in responding to fluctuating demands for steam.

As well, the obsolete controls were replaced with a master programmable regulator for the boiler room and another programmable regulator for each boiler. Several control and reading points were also added, which meant that a boiler operating strategy could be established. Steam production can be optimized as a result of these additions: the controls maintain an optimum production ratio among the four boilers and maximum overall efficiency can be attained.

  • The fourth measure implemented was the recovery of the condensate from two tanks heated by steam coils to feed the hot water unit heaters that heat a workshop and a parts warehouse.

Boiler room control consoles at the Centrale de chauffage de Chicoutimi.

The following table shows the energy and economic savings from the four energy-efficiency measures implemented at the power plant in 2004 and 2005. The total capital cost was $920,290, including professional fees. Given a cost of $10/GJ (37.89¢/m3) for natural gas and $70,020 in financial assistance from Gaz Métro, the payback period is 3.2 years.

Energy and economic savings from the four measures

Description Cost* Savings** (GJ/year) Savings @ $10/GJ*** ($/year) Subsidy Payback period (years)
Boiler combustion heat recovery system $319,310 7,480 74,800 $19,740 4.0
Automatic purge systems and purge energy recovery systems $75,270 5,550 55,500 $14,650 1.1
Oxygen sensor in smoke pipe of each boiler and Programmable automatic boiler regulator $513,170 13,110 131,100 $34,600 3.7
Condensate energy recovery $12,540 390 3,900 $1,030 3.0
Total of four measures $920,290 26,530 265,300 $70,020 3.2

* Actual cost including engineering expenses
** Anticipated savings in 2004 at the time of the decision
*** 37.89 ¢/m3

Guy Desrosiers, eng.
Technical consultant