Energies 2021 , 14 , 1161
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M pulp = M paper − M f iller (2) The pulp used is considered to be a mixture between one type of virgin pulp and RCF pulp, and the mass of each type of pulp was calculated based on r , which represents the mass percentage of RCF in the pulp. M RCF = M pulp · r (3) M virgin pulp = M pulp − M RCF (4) The wood used to produce the virgin pulp (chemical and mechanical) is calculated by using the pulp yield (dry mass of pulp over the dry mass of wood: Equation (5)) of each pulping process (Table 7). Pulp yield = M virgin pulp M wood (5)
Table7. Pulp yield of the different types of pulp considered.
Pulping Process
Pulp Yield [37]
Kraft
50% 45% 94% 94% 85%
Sulfite
Groundwood
Refiner Mechanical Thermomechanical
The absolute heat consumption for each sub-process ( p ) used to produce x is then the product of the specific heat consumption of the process ( h p , x , kWh/t) by the mass output of the process ( M p , t). The specific heat consumption per ton of pulp or paper ( h x , kWh/t) corresponds to the sum of all processes used for production (found in Tables 1–3) divided by the pulp or paper produced ( M x , t): Equation (6). The same calculation is made for electricity ( e x , kWh/t): Equation (7).
∑ M p · h p , x M x ∑ M p · e p , x M x
(6)
h x =
(7)
e x =
This study assumes that the paper mill is equipped with a CHP plant (biofuel and natural gas CHP unit) to generate the required heat and electricity. The power to heat ratio is also considered to be 30% in the CHP unit. 3.2. Mathematical Formulation: Energy and Fuel Consumption of the Entire Industry in Austria The total consumption of heat needed for the total annual production of P&P in Austria of each product ( x , t: pulp or paper) is calculated by the multiplication of the specific heat need ( h x , kWh/t: Equation (6)) for the production of product ( x )with the annual production of the product ( P ) ( P x , y , t). The total heat consumption by the industry ( H y , kWh, Equation (8)) corresponds then to the sum of the heat needed for the production of all products. The same methods are used for electricity consumption ( E y , kWh, Equation (9)), using the specific electricity needs ( e x : Equation (7)) to produce each product H y = ∑ x h x · P x , y (8) E y = ∑ x e x · P x , y (9)
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