Welcome to the MiniMill

By Justin Toland, Contributing Editor

BRUSSELS, Aug. 31, 2008 (Viewpoint) - Big is beautiful in our industry. The 11 m wide PM, the 1 million tonne/yr bleached eucalyptus kraft pulp mill, the 5,000 tonne/day dry solids recovery boiler: these are the benchmarks and the levels to which it seems all aspire.

Yet, sometimes in the rush to scale-up processes, issues affecting existing producers are forgotten – the small mill is left to its own devices or forced out of business. A small, startup company, BioRegional MiniMills (UK) Ltd, is looking to redress the balance and give small (10,000-50,000 tonne/yr), nonwood pulp producers a means of treating their effluent. “No technology is available that can treat black liquor on a small-scale,” explains technical director, MiniMills, Philip Hartwell. “If you want a black liquor treatment plant for a 30,000 tonne/yr straw pulp mill you can’t get one.”

“The main problem with cereal straws is silica,” explains the inventor of the MiniMills technology, Trevor Dean. “[Wheat] straw is 3-5% silica; rice straw is 12% - if you evaporate too much you get glass build up on the inside of the evaporator, which reduces thermal efficiency,” points out Hartwell.

The industrial-scale pilot MiniMill at Radcliffe

“The idea of the MiniMill really came from China,” recalls Dean. In 1993, there were some 10,000 small mills in the country, mostly using rice straw as a raw material. With no means of treating their black liquor, such plants were forced to discharge untreated effluent onto the land or into rivers. “Something like 25% of all water pollution in China was caused by black liquor from straw pulp mills,” notes Hartwell.

Even though the Chinese authorities have closed many of these small mills in recent years (either temporarily or permanently), many still remain. And closing the mills (rather than treating the effluent) creates another pollution hazard: Farmers now burn their waste straw, causing smog.

This lack of a treatment solution led Dean, who has 40 years of international experience in pulping of nonwood fibers, paper manufacturing and pollution control, to begin developing a small-scale chemical recovery process that burns black liquor cleanly to produce heat and energy and directly recover the pulping chemical.

Enter BioRegional

In the 1990s, Dean crossed paths with executive director and co-founder of BioRegional Development Group, Sue Riddlestone (see sidebar). The environmental charity was already involved with schemes to create a sustainable local paper cycle through recycling. But since paper can only be recycled a limited number of times, BioRegional envisaged a future where the recovered fibers would be supplemented with around 50% of locally produced virgin pulp made from local materials such as straw, hemp or coppice wood. The paper produced would then be brought back and recycled again.

As a result, in 1997, BioRegional MiniMills was established to develop and apply Dean’s small-scale, clean technology to pulp straw and recover energy and pulping chemicals from the effluent.

Over the next decade, with the backing of WWF International, the UK government’s Department of Trade and Industry (DTI) and UK agencies such as DEFRA and the Home Grown Cereals Association, as well as paper producers James Cropper, Tullis Russell, Curtis Fine Papers, and Inveresk (whose former CEO, Stefan Kay, is now Chairman of BioRegional MiniMills), the new company designed a complete pulp mill process line for nonwood fibers, with technology that can be readily adapted to wood fiber.

The closed loop process would both minimize discharges to land, air and water while using 50% less energy than a traditional wood pulp mill and 90% less energy than a standard nonwood fiber facility. Water use would be reduced by some 80%, while BioRegional calculates that pulping straw in a 10,000 tonne/yr MiniMill saves 48,000 tonnes/yr CO2 when compared with the current situation in China where pulp is imported and straw burned.

Another advantage, says Riddlestone, would be the reduced ecological footprint: Recycling your paper to the paper mill and buying back again reduces your eco footprint by 93%. Plug a MiniMill into that loop and you further improve the efficiency.

Plant operator, Sergio Blanco-Roseti, checks data from 11 different sampling points

Ahsltrom pilot

After successfully demonstrating the technical and economic feasibility of the process at lab-scale, construction of the first pilot scale MiniMill began in October 2007. The pilot mill is located at Ahlstrom Chirnside’s Radcliffe Pulp Processing Plant in Radcliffe, Greater Manchester, UK. Radcliffe produces some 10,000 tonnes/yr of specialty pulp from abaca fiber for use by Ahlstrom Chirnside’s specialty paper mill in Duns, Berwickshire, Scotland (manufacturers of filter paper – e.g. for tea bags – and hospital disposable products).

Ahlstrom Chirnside invited BioRegional MiniMills to set up at its pulp plant, as it had no means of treating its black liquor. “Radcliffe recycles black liquor to the land – it does have some nutritional value, but everyone recognises it’s not a long-term solution,” explains Hartwell.

Left to right: Engineering assistant, James May, Sue Riddlestone and Sergio Blanco-Roseti

The MiniMill, which started up at the beginning of 2008, is using 10% of Radcliffe’s black liquor in its trials. “We have 11 points to measure temperature and pressure around the whole system, explains MiniMills plant operator Sergio Blanco-Roseti. “The GC also measures oxygen at several points, as well as chemicals such as acetone and methane.”

“So far the practical results have been extremely close to the theory, predicting temperatures to within a couple of percent,” says Hartwell. “In the lab we have had some very high recovery rates with straw pulp. In principle, I don’t see why we can’t have high recovery rates of sodium hydroxide, ” he adds. Dependent on the calorific value of the black liquor it’s also possible to run the plant so it’s nearly energy neutral, comments Hartwell.

Rossendale Process Systems constructed the pilot plant, with Wellmann supplying the evaporator. According to Hartwell, the commercial-scale plant, “Might end up being double the footprint [of the pilot]… We’ve tried to make it as modular as possible.”

Working at this small scale is a big change for Hartwell, who previously project managed the startup of the 1,000 tonne/day Shotton II DIP line in 1997. “It’s a different scale, but this is an enjoyable challenge,” he says.

The business plan

Riddlestone explains that while the initial strategy was to persuade investors in China and India to set up MiniMills, BioRegional is now looking closer to home. “The focus has turned to developing the technology for Western applications and then, once it is proven, selling into China,” explains Hartwell.

This is a realistic aim, believes Riddlestone: “There is 4 million tonnes/yr of surplus straw in the UK [out of 12 million produced].” With the rising price of oil, energy and raw materials, and the price of straw only around £25-30/tonne ($49-59), she believes that, “Small-scale locally produced fiber could be very beneficial.” Wheat straw offers a good alternative to hardwood for printing/writing papers: “It gives you a good, closed sheet,” notes Riddlestone.

A full-scale plant would have around twice the footprint of this pilot facility

BioRegional is also preparing to do trials with Scottish wood this fall. “We hope by the winter we’ll know the results for black liquor for the sulfite and sulfate pulping processes,” says Riddlestone.

“We’re mainly into licensing but we could be into manufacturing,” suggests the executive director. One interesting avenue the company is exploring is the possibility of ‘bolting on’ a MiniMill to an existing wood pulp mill to increase the capacity of the recovery boiler. If this proves feasible, a long-standing obstacle to incremental capacity increase in the pulp sector could finally be overcome. At present, the only way to overcome a bottleneck at the boiler is to invest in a new one, which will of course, enable a large increase in capacity, but which doesn’t come cheap. BioRegional believes its technology may allow an increase of say 10% in recovery boiler capacity at a relatively low cost.

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