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Energy efficiency measures - Industrial - Heat recovery - Pulp and paper

Template assignment

Base Case

• A bleaching agent (ClO₂), at 10°C, is injected into pulp. Steam is then required to increase the pulp temperature before it enters the bleaching towers
• In another process of the plant, hot water is produced from water at 39°C, partly by heat recovery from a process, partly by steam
• Total steam usage is 100,000 kg/h, operating 8,000 h/yr, pressure is 300 psig, temperature is 220°C, there is no condensate return and makeup water temperature is 10°C
• Natural gas fired steam boiler efficiency is 78%
• Natural gas rate is $0.30/m³

Proposed case

• High temperature wastewater (75°C) overflows from the washers at the bleaching process and is used for heat recovery
• Install heat exchanger to preheat the warm water with the bleaching process effluent
  • Hot stream: 9,000 L/min, 75°C, 8,000 h/yr
  • Cold stream: 8,500 L/min, 39°C, 8,000 h/yr
  • Heat recovery efficiency is 71.5%
  • Cost of retrofit is $4,000,000
• Install heat exchanger to preheat the ClO₂ with the cooled bleaching process effluent
  • Hot stream: 2,000 L/min, 51°C, 8,000 h/yr
  • Cold stream: 2,000 L/min,10°C, 8,000 h/yr
  • Heat recovery efficiency is 75%
  • Cost of retrofit is $1,000,000

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.