ESA-186-2 Public Report
The Norpac Foods Stayton plant produces frozen and canned vegetable products. The plant’s operations are seasonal; 67% of the annual energy consumption occurs during the high season months of July, August, September, and October.
Natural gas usage rates range from 9 MMBtu/h in the low season to 43 MMBtu/h in the high season. The plant purchases 100% of its electric demand. The average demand ranges from 2,000 kW in the low season to 6,300 kW in the high season.
The plant is equipped with four natural gas-fired package boilers. Process steam uses include blanchers, cookers, retorts, and heating of sanitation water.
Objective of ESA:
The objective of the Energy Savings Assessment (ESA) was to:
- Perform an abbreviated Energy Savings Assessment using the DOE’s suite of Steam Tools
- Train the staff in the use of the Steam Tools so that they can identify additional energy savings opportunities after the Energy Savings Assessment
- Enable Norpac to apply to other plants the knowledge gained in the Stayton ESA
Focus of Assessment:
Boilers, steam distribution system, condensate return system, and process uses of steam
Approach for ESA:
The approach of the training assessment was to provide training on DOE Steam Tools suite and use them to identify and analyze potential opportunities.
- Identified opportunities and best practices using the Steam System Scoping Tool (SSST)
- Modeled the steam system using the Steam System Assessment Tool (SSAT)
- Used SSAT to estimate savings from opportunities identified in SSST and plant tours
- Demonstrated the use of E3PLUS to evaluate insulation-related opportunities
General Observations of Potential Opportunities:
Annual Energy Consumption:
In 2006 the plant consumed 0.18 TBtu of natural gas and 30,105 MWh of electric energy.
||2006 Consumption (MMBtu)
Energy Savings Opportunities:
The following points should be considered when evaluating the potential opportunities identified on page 1 and described below:
- There is an opportunity to improve the plant instrumentation and data recording systems. This will enable plant staff to gain additional insight into steam system performance and to have greater confidence in the results of the baseline SSAT model and potential energy savings opportunities. There are no steam meters at the plant. Total steam consumption was estimated based on total gas consumption and estimates of boiler efficiency. There was no data available to support the allocation of the estimated total steam flow to the HP and LP headers.
- The estimated savings of most of the individual opportunities described in this report will be influenced by decisions made regarding other individual opportunities. In other words, the total savings will be different than the sum of the individual projects.
- During this training assessment, the plant was modeled in SSAT using annual average data. But because the plant has two distinct operating seasons, it will be useful for Norpac to use the knowledge gained during the training to create two or more models that more accurately reflect plant operating modes.
- The seasonal nature of some energy-intensive operations and the significant distances between some steam system components make it difficult to justify, from an economic perspective, some types of energy savings opportunities.
- There are some energy savings opportunities associated with end-use equipment such as blanchers, continuous cookers, and retorts; however, SSAT is not designed to analyze specific pieces of end-use equipment. To estimate savings associated with these types of equipment, Norpac will have to first perform some non-SSAT analyses. The results of some of those analyses can be entered into SSAT to estimate the economic impacts on the overall steam system. For example, steam demand savings estimated in a non-SSAT analysis of blancher performance or operation can be entered in SSAT Project 1 (Reduce Steam Savings)1.
1 The DOE’s Steam System Assessment Tool (SSAT) includes a number of predefined energy savings opportunities common to many, but not all, industrial steam systems. The opportunities are referred to in SSAT as Projects. Project 1 is simply a reduction in facility steam demand.
Energy Savings Opportunities:
- Change Boiler Efficiency – Flue gas oxygen is measured during the annual tuning of the boiler’s positioning-type air-fuel ratio controller. The controller does not include feedback from an oxygen sensor. There may be an opportunity to improve the efficiency of the boiler by lowering the excess oxygen present in the flue gases. The plant should continue to evaluate the costs and benefits of a robust, automatic control system. If an automatic controller is not cost effective, there may be an opportunity to decrease stack oxygen levels slightly during the annual tuning of the existing controller. For the purposes of the ESA we assumed a potential decrease in boiler flue gas oxygen from approximately 5% to 2.5%. Note: The plant should measure carbon monoxide during the boiler tuning efforts. The presence of carbon monoxide indicates the presence of unburned fuel in the boiler furnace.
- Change Boiler Efficiency – Boiler no. 3 is fitted with a stack economizer. There is an additional opportunity to increase efficiency by adding a stack economizer to one or two more boilers. For the purpose of the ESA we conservatively assumed a potential 90 deg F reduction in stack temperature (from 385 to 295 deg F).
- Change Condensate Recovery Rates – There may be an opportunity to increase the high pressure (125 psig) steam condensate recovery rate to approximately 60% (from 50%) by modifying the piping associated with the steam coil space heaters.
- Implement Steam Trap Maintenance Program – The plant has a relatively small number of steam traps (approximately 30). Nevertheless, there is an opportunity to realize some savings by implementing a steam trap maintenance program.
- Implement Steam Leak Maintenance Program – There is an opportunity to realize some savings by fixing steam leaks throughout the facility. Some of the leaks are at valves and pipe fittings, others are from loose-fitting doors or ineffective water seals on steam blanchers.
- Condensing Boilers for Heating Sanitation Water – There is an opportunity to reduce fuel use by heating sanitation water with small and efficient condensing boilers instead of the relatively large and less efficient package boilers. This project would include the installation of a new 3.5 MMBtu/h condensing boiler and associated electrical connection for a draft fan, stainless steel exhaust ducts, and plumbing. The new condensing boiler would be installed on the sanitation tanks being maintained at 125oF, while the average inlet temperature of the water is 80oF. The new condensing boilers are capable of accepting very low return water temperature that leads to condensing exhaust gases. The boilers and its heat exchangers are fabricated with materials that allow them to withstand the impacts of condensation of boiler flue gases.
- Improve Insulation – Several insulation opportunities were identified using E3+ software.
- Sanitation water tank (125 deg F)
- Tunnel defrost water tanks (3 tanks, 100 deg F, outdoors)
- Tunnel defrost water tank (100 deg F, indoors)
- Blancher water line (6” diameter, 170 deg F)
- Boiler steam valves (8” valves, 10 pcs.)
- Continuous cookers
- Boiler blowdown lines
- Chill water lines (6”)
- Multiple Boiler Optimization –There is an opportunity to develop a systematic approach to boiler operations that ensures that steam demand is always being met with the most economical combination of boilers. Such a system was once installed at Norpac but, for reasons that are not clear, the system has been out of service for many years.
Other Options Considered:
Several potential energy savings opportunities were found to be impractical or uneconomic.
1. Change Boiler Blowdown Rate - Boiler makeup water quality and the low condensate return rates associated with this plant’s type of end use equipment contribute to a current blowdown rate of approximately 10.5% of the feedwater flow rate. There may be a cost- effective opportunity to reduce the boiler blowdown rate from 10.5% to 3.0% using either softener chemicals or a reverse osmosis (RO) system; however, our initial and informal cost estimates for these systems led us to conclude that they may be uneconomic. The plant should further investigate the existing controller set-points and the costs of softener and RO systems to determine the economic merits of reducing the boiler blowdown.
The following turbine-related projects were considered and rejected because the economics are unfavorable:
2. Install a combustion turbine (gas turbine) and heat recovery steam generator
3. Install a condensing steam turbine generator or steam turbine driven chiller
4. Install a backpressure steam turbine generator or steam turbine driven chiller
The potential energy savings opportunities summarized on page 1 include estimated time horizons for implementation. The opportunities are categorized as near-term, medium-term, or long-term according to the general guidelines below.
- Near-term opportunities include actions that can easily be attained in less than one year. Examples include improvements in operating activities, equipment maintenance, and relatively low cost actions or purchases.
- Medium-term opportunities would typically require one to two years to implement and would require additional engineering and economic analysis. Examples include capital equipment purchases and moderate changes to the plant’s steam system or processes.
- Long-term opportunities typically require two to five years to implement. Examples include new technologies or significant changes to either the steam system or the plant’s processes.
||% of Savings Opportunities
Management Support and Comments:
The Stayton plant production manager and Norpac corporate engineer participated in this Energy Savings Assessment. Their active participation and collective experience made this a productive ESA. The Norpac team will continue to use the DOE suite of steam tools to quantify additional energy savings opportunities in Stayton and at other Norpac facilities.