PPI (PULP & PAPER INTERNATIONAL) MAGAZINE: The power of waste

Distributed power generation from paper industry residues through gasification

February 2007
By Martin Kay

Escalating costs associated with the purchase of energy and disposal of waste are requiring the paper industry to examine closely opportunities for small scale distributed power generation fuelled by paper industry rejects. This article reviews the challenges faced by the paper industry in diversifying its energy supply while generating revenue from wastes, with a focus on:

• Sources, quantities and types of waste generated
• Available advanced technologies
• Challenges for distributed power generation in the paper industry.

Energy prices

According to CEPI's recent Report on the Competitiveness of Europe's Pulp and Paper Industry: The State of Play, energy accounted for 13% of the cost structure of the European paper industry in 2005 -- with prices increasing by 61% from 2004 levels. In the UK, increased energy prices have resulted in the closure of marginal production units, particularly lower tonnage operations that manufacture commodity grade paper and board products.

Fig. 1 - The gasification process

Waste generation and waste management

The European paper industry has taken a leading role in recovering and recycling paper. For instance, the amount of recovered paper used by UK paper mills as a proportion of their total output is 72%, a figure believed to be close to the maximum achievable given the present mix of products. As a downside, these operations are prone to produce various by-products including deink and primary sludge (which in the UK are mainly landspread), together with plastics rejects and 'stickie-laden fiber clumps' that are disposed to landfill, Table 1.

The potential of gasification

There is growing interest in small-scale distributed power plants fuelled by paper industry wastes. A typical application would be a combined heat and power (CHP) plant with an electrical output of approximately 250kWe, small footprint and scalable, consuming circa 400 kg/hr (10 tonnes/day) of feedstock. These modules can be multiplied economically to handle up to 3,000 kg/hr (48-72 tonnes/day). These reject values equate to a mill/machine producing up to 300,000 tonnes/yr.

Currently, one of the advanced technologies for distributed power generation is the fixed bed downdraught gasifier coupled to a mass-produced internal combustion engine.

Gasification is the conversion of biomass (a renewable source of fixed carbon) into a fuel gas (called a 'producer gas') that can be used in heat, power or combined heat and power applications. The process of gasification has also been called 'starved combustion'. Unlike combustion, no NOx (nitrogen oxide) or dioxins are generated in the process. Depending on the fuel composition, the generation of other emissions such as SOx (sulphur dioxide) is extremely low (<10ppm).

A downdraft gasifier converts prepared fuel into producer gas, which is then conditioned to remove traces of 'tars' and dust particles before being cooled and supplied to a gas engine -- either a modified diesel engine or a liquified petroleum gas (LPG) engine. The complete system consists of biomass handling (conveying, drying and feeding), gasification (gasifier, char and ash removal, gas conditioning and cooling, gas storage) and power generation (single fuel gas engine or modified diesel engine).

Example

A mill or machine that produces 100,000 tonnes/yr of paper from recovered fiber generates rejects available as the feed input fuel to a gasifier, Table 3.

The estimated net income (avoidance in disposal to landfill estimated at Euro 85/tonne, together with income generated from the sale of renewable electricity, estimated at Euro 0.11/KWh generated) is attractive. It is estimated that initial investment will be returned within three years, Table 4.

Challenges to overcome

Distributed power generation that converts paper industry residues into 'energy' is attractive to paper companies seeking to reduce costs and demonstrate the sustainability of their manufacturing process. However, key challenges remain:

• To recommend feedstock preparation and management of ash
• To quantify the energy recovered through gasification of a range of paper industry wastes with variable calorific value
• To identify the advantages of gasification to the paper industry (over other thermal technologies)
• To undertake an economic analysis and determine payback on investment
• To examine the potential for the paper industry to contribute to 2010 targets for 10% of electricity from renewable sources (or 2020 targets of 20% of electricity from renewable sources).

To examine routes to fully operational distributed power generation for the paper industry, including grid connection, intelligent network management and methods to convert intermittent generation to controllable sources of electricity.

Dr Martin Kay is Head of Paper and Research, Pira International, Cleeve Road, Leatherhead, Surrey, KT22 7RU, UK. For further information, email: martin.kay@pira-international.com

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