A substantial amount of steam is produced as a by-product of thermo-mechanical pulping – amounts reaching 0.8 to 0.9 t/t-pulp, or around 2/3 of the power input to the refiner (NEDO, 2008. p. 166). This low pressure steam is usually contaminated but its heat content can be reclaimed for use in other processes. Heat recovery options include:
TMP heat recovery is applicable to any mill that uses pressurized refining and currently does not use heat recovery – which usually means older mills, because most modern TMP mills are designed with heat recovery systems ((Kramer et al., 2009. p.99).
Typically, between 1.7 to 2.5 MWh/t of energy is used in refiner main lines. The theoretical maximum values for recoverable energy flows from this is given in the table below:
| Source of Energy Recovery | Single Disc and Conical Disc Refiners (as %) | Twin and Double Disc Refiners (as %) |
|---|---|---|
| High pressure steam recovery | 61 | 79 |
| High pressure steam condensate | 11 | 15 |
| Low pressure heat recovery | 20 | Not applicable |
| Low pressure condensate | 2 | Not applicable |
| Irrecoverable heat (e.g. due to low value heat in fiber and water, motor cooling losses, radiation losses) | 6 | 6 |
| Development Status | Products |
|---|---|
|
Commercial
|
| Parent Process: Mechanical Pulping | |
|---|---|
| Energy Savings Potential |
One study estimates heat recovery systems for pressurized refiners can generate 1.1 to 1.9 tons of clean steam at dryer pressure per ton of pulp (Kramer et al., 2009. p.99).
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| CO2 Emission Reduction Potential |
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| Costs |
Average installation costs have been estimated to be $21/t-pulp (2000 dollars), with significant increases in operation and maintenance costs. |
This Energy Guide discusses energy efficiency practices and energy-efficient technologies that can be implemented at the component, process, facility, and organizational levels.
This revised 2008 version of the publication from New Energy and Industrial Technology Development of Japan includes information on innovative Japanese technologies for energy efficiency and for the reduction of CO2 emissions.
For a 150 tpd plant, recovery of 695 GJ of energy in the form of steam and 1175 GJ of energy in the form of hot water is reported (NEDO, 2008. p.166)