Cost savings – fuels

As illustrated in Fig. 44 fuel cost savings are broken down into consumption savings ( 5.2.1.1) and price savings ( 5.2.1.2). As the latter refers to the average price of the consumed fuel mix, it also comprises the variations in the fuel mix – at constant requirement of total primary energy.

5.2.1.1 Cost savings – fuel consumption

As described in 2.1.3.2 for the pulp and paper industry in general and in 4.2.2.1 for the investigated mills in particular, more than 85% of the fuels consumed are used for generation of steam in boilers, less than 15% provide direct heat (e.g., lime kiln, IR-drying). In order to maximise the yield from the fuels, the steam is typically generated at high energetic conditions (> 450°C, > 60 bar) and relaxed in back-pressure turbines to process requirements.

As this procedure of combined heat and power generation is absolutely reasonable – it decreases the average costs (price) of electricity – the primary steam consumption of the turbines is left untouched in this chapter. Considerations of the electricity yield from this steam are made in chapter 5.2.2.2. Chapter 5.2.1.1 rather focuses on the consumption of process steam and direct heat, the recovery of heat from the process, and the yield of primary steam from fuels. It closes with a brief discussion of the advantages and disadvantages of direct heating vs. steam heating.

5.2.1.1.1 Cost savings – consumption of steam and direct heat in the process

(1) Save fuel costs reducing consumption of steam and direct heat automating monitoring, controlling, and steering

The implementation of a comprehensive system of monitoring steam and direct heat supply, transfer and consumption is the first step towards fuel saving. Leakages in pipes and steam traps (separating live steam from condensed steam and non-condensable gases) are reported immediately and can be repaired quickly (Martin et al., 2000). Variations in consumption will be observed and scrutinised. Thus, simple measuring evokes changes in the behaviour of the personnel. Manual process control should be replaced by automated process control (Commission of the European Communities, 2001). The steering of continuous or repeated processes should also be automated as far as possible. Martin el al. (2000) estimate about 7%

savings of thermal energy at paper drying by using IR-profiling to measure the moisture content, fibre orientation etc. in the steering of the paper machines' press and drying sections.

Steinbrecher and Hahn report similar fuel savings for gas-fired IR-dryers in coaters. Another application for automated steering is the airflow in the drying section of the paper machine. If automated steering reduces the air flow to an amount that the exhaust air is close to its dew point, not only is the electricity consumption minimised but also the heat recovery from the exhaust air becomes more effective (Commission of the European Communities, 2001). The

initial investment in automated monitoring, control, and steering equipment typically pays off within a relatively short time. Recurring costs are comparably negligible.

Range of application: All pulp and paper mills with steam or direct heat consumption Ease of implementation: High

Magnitude of impact: Low

(2) Save fuel costs reducing consumption of steam and direct heat through regularly maintaining equipment

The second action is a typical good practice measure again. Regular and properly accomplished maintenance allows energy savings in many process steps of pulp and paper manufacturing. Martin et al. (2000) estimate 3% savings in the overall fuel consumption by regularly inspecting and maintaining the steam distribution system. Minor leaks are observed more quickly and major leaks can be avoided. Other examples for saving steam or direct heat through proper maintenance are wires and felts in the wet section of the paper machine. If they are cleaned regularly and replaced when appropriate, the web dewaters better in the wet and press sections and a higher dry solids content at the beginning of the drying section can be reached. This action has basically no investment costs and current savings regularly exceed costs of maintenance.

Range of application: All pulp and paper mills with steam or direct heat consumption Ease of implementation: Very high

Magnitude of impact: Low

(3) Save fuel costs reducing consumption of steam and direct heat through minimising production interruptions

The third action is also self-explanatory: as heat gets lost with any production interruption, all equipment-specific measures safeguarding good runability and minimising production interruptions save heat and thereby fuels. This is a typical problem of older and fast-running paper machines, where the web breaks frequently and subsequent run-ups take up to 30 minutes. Not only does the pre-dried paper get lost and is dissolved in the white water, significant heat losses also originate from the steam-heated drying cylinders in the dryer as convection or radiation (Commission of the European Communities, 2001). Measures to reduce production interruptions are favourable not only due to energetic reasons. Any production loss is also typically regarded as a loss in turnover and profit.

Range of application: Especially older and fast-running paper machines Ease of implementation: Medium

Magnitude of impact: Low

(4) Save fuel costs reducing consumption of steam and direct heat through improving insulation

Digesters, bleaching equipment and, if applicable, also pulp dryers are the heaviest steam consumers in pulp manufacturing, the drying section of the paper machine and potentially also the succeeding coating equipment are the correspondents in paper manufacturing. Steam is typically provided to all these consumers in one or two process steam grids. An improvement in the insulation of grids as well as consumers allows significant savings of steam and, thereby, fuels. Steinbrecher and Hahn (2003) have discovered considerable potential in the steam grids. Martin et al. (2000) suggest heat savings through improvements in insulation of existing continuous digesters in chemical pulping. De Beer et al. (2001) put emphasis on the drying hoods of paper machines. They stress that a dew point increase by about 4°C allows significant reduction of ventilation air (see also action 1). The financial favourability of improving insulation of existing steam grids and consumers needs to be calculated case by case. Steam savings can usually only be achieved by significant investments.

Range of application: All mills; especially chemical pulp mills and paper mills Ease of implementation: Medium

Magnitude of impact: Low

(5) Save fuel costs reducing consumption of steam using advanced technology at cooking Advanced cooking processes offer potential for significant steam and, thereby, fuel saving in chemical pulping. However, yield and pulp properties need to be observed and are at least as important as steam consumption. Martin et al. (2000), referring to Elaahi and Lowitt (1988), regard pulping in alcohol-based solvents (ethanol-water solution) as a potential future alternative to traditional kraft pulping. They report significant yield increases at reduced cooking times. The cooking process they describe removes 75% of the lignin in a first cooking stage and the remainder in a second stage (liquor extraction). The alcohol is largely recovered by steam stripping but is still a very costly cooking medium. Furthermore, a small amount of additional fuels is needed. This process tends to offer large potential in yield as well as in steam consumption. However, its feasibility on an industrial scale and commercial favourability still need to be proven. Nevertheless, it can be assumed that modified or newly developed cooking processes will replace some of the current processes due to a better combination of pulp properties, yield, and pulping costs.

Range of application: Chemical pulp mills Ease of implementation: Low

Magnitude of impact: Medium