Becoming more energy efficient

See Key material issues – Bio-energy, for more information about Ngodwana Energy, the biomass project in which we have a 30% shareholding.

Overview

Our aim is to enhance energy self-sufficiency, improve energy efficiency and decrease our reliance on fossil fuels. We are achieving this by making process changes, installing best available technology (BAT) which is more energy efficient, reducing purchased energy (electricity and fossil fuel) by increasing our use of renewable energy―an approach that ultimately results in a reduction in CO2 emissions.

As can be seen from the graph below, specific energy intensity has steadily decreased over time.

Specific energy intensity (GJ/adt)1

Saleable production (adt/a | Graph

1 Figures based on net calorific values.

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Renewable energy

Our renewable energy consumption in 2018 was 46.8% of total energy consumption, 71.5% of which was derived from black liquor, as indicated in the pie chart below. The regional renewable energy profile is as follows: SEU: 25.3%, SNA: 79.3% and SSA: 42.7%.

Group renewable energy consumption (%)

Group renewable energy consumption (%) | Graph

Using renewable, rather than fossil fuel, energy sources is important, as the burning of fossil fuels releases ‘new’ CO2 previously locked up in the earth’s crust in the form of oil, gas or coal. When renewable energy like biomass is burned, the CO2 released is equivalent to that which was bound from the atmosphere during the process of photosynthesis―so, no ‘new’ carbon is being introduced.

The reason for the much higher percentages of renewable energy in our mills in SNA and SSA than in SEU is that in the first two regions, a much greater proportion of our product originates from integrated pulp and paper mills. These mills typically have a higher degree of energy self-sufficiency than mills with different processes from those that only produce paper, as the black liquor (dissolved organic compounds from wood) created during the manufacture of pulp is a biofuel and a primary source of renewable fuel for steam and power production.

While we are committed to higher use of renewable energy, we have the following process constraints:

  • Currently, our black liquor recovery boilers and chemical recovery plants are used to maximum capacity and any additional black liquor is sold
  • There are constraints in the existing infrastructure which limit the use of biomass including low capacity of receiving stations and feeding systems
  • The use of biomass in existing coal-fired boilers is limited as these boilers are designed for hard coal, given that the operation of the installed steam turbines requires higher inlet heat loads, and
  • In SNA, our combustion of biomass is constrained by the scarcity of drivers who can make deliveries. In addition, increasingly limbs and toppings are increasingly being diverted for use on logging roads to limit erosion, instead of being sent to our mills.

Renewable energy (%)1

Group renewable energy consumption (%) | Graph

1 Renewable energy certificates (RECs) not deducted.

Comment:
Across the group, renewable energy was stable, but decreased in SEU due to unplanned maintenance standstill of the green power steam generator turbines at Alfeld and Stockstadt Mills. It also decreased at Gratkorn Mill because of increased consumption of natural gas for power and heat generation―the result of a cold winter. In SNA, all three mills showed slight decreases. Westbrook Mill increased coal firing for economic reasons while Somerset Mill increased their use of natural gas and #6 oil in response to low biomass inventories. These were partly due to a woodroom replacement capital project and economic pressures. In SSA, there was a slight increase due to the inclusion of Lomati Sawmill which has a high energy self-sufficiency and a slight increase at Saiccor Mill. The latter was due to an increase in the amount of black liquor fired and a decrease in heavy fuel oil consumption as a result of enhanced boiler operation stability.

Energy self-sufficiency (%)

Energy self-sufficiency (%) | Graph

Comment:
Across the group, there was a slight increase. In SEU, energy self-sufficiency was stable. Maintenance standstills of steam turbine generators at Alfeld and Stockstadt Mills reduced energy self-sufficiency. However, this was compensated by an increase in energy self-sufficiency at Ehingen and Kirkniemi Mills. In SNA, there were a slight decrease. Somerset Mill showed a decrease due to additional power boiler and turbine outages resulting from boiler water pH excursions. In SSA, there was a slight increase due to the inclusion of Lomati Sawmill which has a high degree of energy self-sufficiency; as well as an increase in black liquor fired and a decrease in heavy fuel oil consumption as a result of more stable boiler operation at Saiccor Mill. At Ngodwana Mill, energy self-sufficiency increased due to good performance of the recovery boilers, increased bark combustion and more efficient steam usage.

Fuel sources (%)

Fuel sources (%) | Graph

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Energy consumption within organisation (GJ/a)

Energy consumption within organisation (GJ/a) | Graph

Energy intensity (GJ/adt)1

Energy intensity (GJ/adt) | Graph

1 Figures based on net calorific values.

Comment:
Across the group energy intensity based on specific total energy (STE) (GJ/adt) was stable. In SEU, while Kirkniemi Mill increased production by approximately 10%, resulting in a decrease in energy efficiency, Lanaken Mill experienced operational problems with its gas turbine in 2017. However, in 2018 operations resumed as normal, with the mill reducing specific natural gas consumption. In SNA, there was a slight decrease. Cloquet Mill continued to improve due to a combination of stable production capital projects and Lean Six Sigma efforts. This offset increases at Somerset Mil due to the rebuild of PM1 and at Westbrook Mill due to power generation inefficiency. In SSA, energy intensity decreased slightly. This was due to the following actions: At Stanger Mill, coal savings were achieved because of the optimisation of airflow, grate speeds and guillotine heights on boilers, as well as improved insulation lagging. In addition, there were electricity savings due to installation of high efficiency lighting mill-wide and load shedding the wash press during peak periods. At Tugela Mill, energy intensity decreased due to above-budget saleable production and improved efficiencies. The mill stopped one refiner on PM2, made improvements to the digester (energy saving of 164 KW/h per ton), stablished the spray dryer and reduced steam consumption. In addition, a vacuum pulp commissioned after the shut contributed positively, as did energy conversion on the gas boilers. Coal savings were achieved as the turbine maximised generation. At Ngodwana Mill, the reduction was due to efficiency improvements in steam usages and good performance of the recovery boilers in Q4.

Black liquor, which is classified as a biofuel, is the spent cooking liquor from the pulping process which arises when pulpwood is cooked in a digester thereby removing lignin, hemicellulose and other extractives from the wood to free the cellulose fibres. The resulting black liquor is an aqueous solution of lignin residues, hemicellulose and the inorganic chemicals used in the pulping process. Black liquor contains slightly more than half of the energy content of the wood fed into the digester.
In South Africa in 2018, Sappi signed an agreement with the Department of Energy to build a 25 MW biomass energy plant at Ngodwana Mill in Mpumalanga
Sappi will have a 30% stake in the facility, which is expected to contribute to the national grid from 2020 (see Key material issues – Bio-energy).
Gratkorn Mill has partnered with local energy provider Bioenergie Wärmeservice GmbH (BWS) to supply industrial waste-heat
generated by the mill’s combined heat and power (CHP) plant to Energie Graz for the next 20 years. Transported to Graz via nine kilometres of underground pipes and at a temperature of 120° C, the excess heat is fed into the city’s existing heating system and
will be used to keep 18,000 households in the Austrian city of Graz warm.
As a result of this initiative, total CO2 emissions will be reduced by 20,000 tons per annum.