Abstract

Paper production is an energy intensive industry but due to the wastes of its process (black liquor, waste biomass, sludge) has the capacity to generate most of its energy internally. Central to this balance are cogeneration units that guarantee the internal production of heat and electricity. These are sized for the company’s thermal load, with excess electricity injected into the grid.

The efficient use of endogenous resources is a major route for improving the energy and environmental efficiency of the plant. Some of the waste materials include biomass wastes, sludges and other industrial wastes such as plastics.

The present work aims to identify the opportunity of introducing a waste biomass gasification plant and the use of the produced synthesis gas, replacing the natural gas currently used in the turbine included in the company’s cogeneration unit.

In this scenario, one of the cogeneration units in its current configuration has two steam boilers (one biomass; one black liquor) and a gas turbine whose waste heat feeds a recovery boiler to produce steam.

The work involved several steps: the energy balance of the unit, the characterization of biomass residues (mixing bark, pine bark, eucalyptus bark, and refuse fibers), the test experimental analysis of residual biomass gasification and the characterization of the synthesis gas produced.

In the electric and thermal energy producing units, gas turbines have a working efficiency above 35% while the steam turbines is considerably lower (15%). The efficiency of the chemical recovery boiler (79.5%) is lower than that of the biomass boiler (89.5%).

From the experimental analysis of biomass it was found that most of them have a carbon and hydrogen content higher than 48 % and 5 %, respectively. In terms of higher calorific value (HHV), for the biomass where it was possible to determine it, the value is between 19.3 and 23.6 MJ/kg. These properties reveal that the selected biomasses from within the company, have potential as fuels. The limitation on its use may be due to the ash content, which tends to exceed 10 %.

A gasification test (90 % eucalyptus biomass and 10 % mixture biomass) was also carried out to produce syngas and further characterization. The calorific value of the gas produced was 18 MJ/kg, with an absolute density of 1.17 kg/m3.

It can thus be seen that for a gas turbine with a 35.8 % efficiency with a workload of 29.9 MWe 4.6 kg/s of syngas is required.

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