Energy efficiency measures - Industrial - Heat recovery - Dairy
Template assignment
Base Case
Proposed case
Template assignment
Base Case
- In a dairy plant, raw milk is preheated from 5ºC to 40ºC in a regenerative heat exchanger using hot pasteurized milk coming out from the pasteurization holding tube at 74 ºC reducing its temperature to 35ºC
- After the cream separator, the milk is further heated from 40ºC to 74ºC using hot water
- Milk heating load is 445 kW, duty cycle is 100%, operating 5,400 h/yr
- Natural gas boiler seasonal efficiency is 70%
- A whey stream is cooled from 30ºC to 5ºC using chilled water
- Whey cooling load is 262 kW, duty cycle is 100%, operating 5,400 h/yr
- Chiller seasonal coefficient of performance is 3.0
- Natural gas rate is $9.7/GJ, electricity rate is $0.05/kWh
Proposed case
- (1) A new heat exchanger is installed to preheat the raw milk using the whey (the original regenerative heat exchanger is relocated after the cream separator)
- Hot stream: whey, 30 ºC, 12,000 kg/h (3.24 L/s), 5,400 h/yr
- Cold stream: raw milk, 5 ºC, 12,000 kg/h, 5,400 h/yr
- Heat recovery efficiency is 80%
- Heat exchanger reduces the load on the refrigeration system to cool the whey previously done by chilled water
- Heat exchanger preheats the milk to 25 ºC, heat recovered from this heat exchanger replaces existing recovered heat in base case scenario
- Cost of new heat exchanger is $90,000
- (2) A second heat exchanger is installed to further preheat the raw milk using the precooled pasteurized milk from the regenerative heat exchanger
- Raw milk is heated from 25 ºC to 40 ºC using 50 ºC precooled pasteurized milk
- Cost of new heat exchanger is $60,000
- Heat recovered from this heat exchanger also replaces existing recovered heat in base case scenario
- (3) The existing regenerative heat exchanger is relocated after the cream separator to heat the skim milk using the pasteurized milk
- Hot stream: pasteurized milk, 74 ºC, 12,000 kg/h, 5,400 h/yr
- Cold stream: skim milk, 40 ºC, 12,000 kg/h, 5,400 h/yr
- Heat recovery efficiency is 70.5%
- Cost for relocation and modification of existing heat exchanger is $60,000
- Assume milk heat capacity of 3.93 kJ/kg/ºC and density of 1,030 kg/m3
Base case
Proposed case
Solution
The worked-out solution is the data file selected from within the RETScreen Project Database. The user automatically downloads the Project Database file while downloading the RETScreen software.
The worked-out solution is the data file selected from within the RETScreen Project Database. The user automatically downloads the Project Database file while downloading the RETScreen software.
