Optimizing facility operations with cogeneration systems
Applied Medical Resources optimized operations by integrating cogeneration equipment into its facility.
- Realize the facility operation's improvements with cogeneration systems
- Understand performance data to meet facility requirements
- Explain design considerations for cogeneration systems.
A cogeneration system is not a single technology, but an integrated energy system that can be modified depending upon the needs of the energy end user. This type of system burns natural gas to simultaneously produce electricity and heat (see Figure 2). The heat is recovered from the combustion system's exhaust stream and converted into useful thermal energy, in the form of steam or hot water, which is either used directly or fed into an absorption chiller to provide cooling.
Expanding manufacturing with onsite generation
Applied Medical Resources (AMR) was moving its manufacturing equipment into a larger facility and expanding its manufacturing capabilities. The company was interested in providing onsite generation for the two new buildings and central plant located in Lake Forest, Calif. The larger building is used for manufacturing injection-molded parts and operates around the clock with the exception of 2 days per year. The smaller building houses offices and manufacturing support spaces. A bridge structure between the buildings houses the chiller, boiler, and cooling tower systems that serve the HVAC and process cooling/heating loads. The onsite generation equipment would be located in the bridge equipment area.
The manufacturing equipment consisted of existing units that would be relocated as well as new units. Space for future growth was provided. To evaluate the initial and future power requirements of the facility, AMR provided electrical data for the existing manufacturing building currently housing the manufacturing equipment that would be moved. Fifteen-minute data for April 1, 2011, through June 26, 2013, was used to determine the facility's base electrical load. Monthly data for January 2004 through August 2013 was used to estimate future expansion and increases in electrical load.
The 15-minute electrical data was used to determine the minimum facility load. The four data points for each hour were averaged to obtain the hourly average kilowatts. These averages were then binned in 50-kW increments to determine the percentage of the time the facility was operating within each bin (see Figure 3). It was found that the current injection molding facility operated at 500 kW or less approximately 96% of the time. The maximum facility load during the period was 1,085 kW and occurred less than 1% of the time.
The average kilowatt data for each hour was then analyzed to determine if there were significant differences in weekday and weekend usage. Three day types were used: weekday, Saturday, and Sunday. For each hour, the kilowatt data was averaged by day type (see Figure 4). There was not a significant reduction in usage between the day types. The weekday usage was typically the highest, followed by Saturday and Sunday. In all cases, the average kilowatt measurement was greater than 500 kW.
Based on Figures 3 and 4, a cogeneration system with a 500-kW initial capacity could be operated continuously at nearly full capacity.
Facility growth with cogeneration systems
Future growth also was considered. AMR intended to maintain the rate of growth they had experienced over the previous 5 years. The monthly electrical data was used to calculate the year-over-year increase in consumption (kWh) and demand (kilowatts) for each month and for each year as a whole. The average year-over-year growth factor for consumption was 1.10 kWh and for demand was 1.19 kW. Using this data, the required minimum generation capacity would increase to approximately 1,100 kW in 5 years.
While meeting the facility electrical needs was the primary focus, it was important to understand where the cogeneration system's heat recovery could be used and to determine the associated minimum load. A process cooling-water system provides a consistent 24-hour load that can be served by the waste heat recovery associated with the cogeneration system. To quantify this load, temporary data collection equipment was installed on the current system in the existing manufacturing building. The system flow, supply temperature, and return temperature were trended on 1-minute intervals.
The tonnage for each 1-minute interval was calculated using the flow and temperature difference data as shown in Table 1. The average hourly tonnage was calculated for each hour by summing the interval data and dividing by the number of intervals. This average hourly tonnage data was used to develop a typical daily load profile for the process cooling-water system. The future growth in process cooling load was assumed to occur at the same rate as the electrical load. All of the observed existing equipment required process cooling water, and future growth in the manufacturing building is directly related to the addition of equipment. A 10% year-over-year growth results in a minimum requirement of 90 tons.
AMR also wanted the system to provide standby power during an extended blackout. The cogeneration system would need to be capable of operating in an "island mode" in a manner acceptable to the electric utility and in compliance with the current code requirements. Island-mode operation of a generator is defined as a generator capable of self-excitation and black start, for supplying power to a distribution system that is electrically isolated from the local utility power supply.