Energy: Use it carefully
By Pulp & Paper Canada
IF ONLY all Friday sessions could be as well attended as the Energy Committee sponsored session. The first of five papers was a study of the new No. 19 power boiler at Pacifica Papers, Powell River, B...
By Pulp & Paper Canada
IF ONLY all Friday sessions could be as well attended as the Energy Committee sponsored session. The first of five papers was a study of the new No. 19 power boiler at Pacifica Papers, Powell River, BC, written by James Utt of Foster Wheeler, and Lloyd Ryan of Pacifica.
The boiler is Canada’s largest biomass-fired bubbling fluidized bed (BFB) boilers (Pulp & Paper Canada, July 1997, p. 16).
Utt said there were many drivers for the project. These included: reducing mill costs by $20/t; the need for more steam and power; reduced fly ash, odor and noise; a reduction in natural gas use; an alternate non-condensable gas (NCG) incineration site; reduced greenhouse gas generation; lower boiler maintenance costs; an opportunity to recycle boiler ash. The new boiler allowed the mill to retire three old high-maintenance boilers.
The emission criteria for the new boiler are: less than 50 mg/m3 salt free particulate emissions, equivalent to an 85% reduction; less than 240 mg/m3 NOx; and, an invisible plume.
The boiler uses hog fuel and sludge (up to 15%) but can also burn 100% natural gas. It is designed to produce 265.3 t/h of steam. The moisture range of the fuel goes from 51 to 64%. due to the high salt content of the fuel (3%), alkali is monitored continuously. One shutdown was necessitated by high salt content coupled with higher than average ambient temperatures that led to dryer fuel. This led to scaling of the grid nozzles.
S. Schroderus, H.A. Simons, discussed upgrading lime kilns and causticizing plants. Why upgrade? There may be many reasons: more capacity, reduced operating costs, improved environmental performance, to meet future needs.
Schroderus noted that the causticizing plant flowsheet has not changed much in the last 30 years.
Pressure disc filters have been introduced over the last 10 years. These are the favorite for new kraft mill projects or major causticizing plant upgrades. They give very clean liquor and suspended solids levels of less than 200 ppm.
Green liquor filtering has also made an appearance in the last 10 years. There are two types: cross flow filtration (falling film) and cassette (pressure tube) filters. There are many mill applications of green liquor filtering but most of them are in Europe. One major benefit is very clean green liquor, essential for closed cycle operation.
When considering slaker and causticizer upgrades, mills should remember that these could be difficult; lay-out can be a problem. Schroderus advised mills to retain single-line operation and gravity flow.
When looking at a lime kiln project, Schroderus said it is important that mills study many facets as a single entity. These include production capacity, mud filtering, back end devices (electrostatic precipitators, scrubbers, cyclones) and lime kiln internals.
No matter what, mills should study several options to find the right solution and plan for future needs. A clear, long-term plan is needed.
W.J.M. Douglas, McGill University, described Integrated pressing and drying simulations of PM 7, Domtar Windsor. Domtar wanted to increase production of PM 7 at its Windsor, QC, mill by increasing machine speed by 25% by modifying the press section. The company did not want to touch the dryer section.
PM 7 produces 1600 t/d of 75 g/m2 fine paper. The base sheet is 72 g and coat weight is 3 g. Douglas explained how the Dryer Doctor pressing-drying simulator, developed at McGill, allows the integrated analysis, design and optimization of the two processes.
Using the multiple technique drying simulation, Douglas said the project involved running about 30 models through the simulation program. These included an extended nip press in the third press section running at different loads, the removal of the fourth press and the installation of a steam box between the second and third nip. The project also involved looking at other guidelines to meet the objective, i.e., lower base weight/higher coat weight.
In conclusion, Douglas said that by running the sheet in its current formulation and without changing the dryer section, the 25% goal could not be met. If the mill went to a 59-g base sheet and a heavier coat weight, it could improve production by 25% but non-contact drying after the size press would be needed, the cost of which was not part of the research team’s mandate.
With an extended nip press and steam box, using a 69-g base sheet, the mill could meet its 25% objective with a payback of just over two years. In response to a question, Douglas said that non-contact infrared drying can be integrated into the model.
Alan Buchkowski, Novadyne, described a newly-developed pulse combustion dryer. One of the first examples of the pulse combustion principle was buzzbomb of World War II. Why apply it to drying? Because of the pulsating gases, very sticky materials can be injected. The gases break them apart. The combustor is simple, compact and inexpensive, according to Buchkowski. When asked about explosions, he said that they “pushed the envelope” in pilot plant tests and had none nor did they have any fires.
A one-million Btu transportable unit was used and a five-million Btu unit is under development. The estimated cost of removing a tonne of water is $8.50 to $11.
The final paper of the session was co-authored by Heikki and Eva Mannisto, Ekono Inc. It dealt with the effect that the Kyoto Agreement on greenhouse gases would have on Canada’s forest products industry. Coming into effect in 2010, the gas levels must meet 1990 figures less 10%. However, because of many conservation measures already taken, the projected CO2 emissions in 2010 only exceed the limit by 12%. The required reduction in CO2 to meet the standard is 2.9 Mt CO2/y. There is significant opportunity for fossil fuel reduction — energy conservation, back pressure power generation, installation of gas turbines.