Heuristic Engineering Inc.

3040 West 5th Avenue, Vancouver, B.C. V6K 1T9  Canada

Phone: (604) 263-8005  Fax: (604) 263-0786 Email: info@heuristicengineering.com

Converting refuse to energy in the 21st Century

Applications

Direct-fire applications without power generation.

1. Direct fire lime kilns in pulp mills

A 60 Million Btu/h unit direct-firing a lime kiln in a BC pulp mill with the 2,200°F (1200°C) products of combustion of 55% moisture content (wet basis) wood residue. Lime availability when fuelled by the products of combustion of wood is the same as when fired by the products of combustion of Bunker C.

3. Direct fire lumber dry kilns in sawmills

A lumber dry kiln heating system in BC showing a 15 Million Btu/h unit direct-firing 2 dry kilns with the 2,000°F products of combustion of wood residue.  The 2,000°F gas stream is blended down to 1,100°F (600°C) with recirculation air drawn from the 2 kilns.

2. Direct fire hot oil generators for dry kiln heat in sawmills.

Click on drawing for enlarged image

A waste-disposal/energy-recovery system proposed for a large sawmill located on a major river in BC. A 60 Million Btu/h hot oil generator is fired by the 1,900°F (1040°C) products of combustion of 63.5% moisture content wood residue. The hot oil is used to dry lumber in the sawmill's 5 large dry kilns.

All the sawmill's residue  is disposed in two 60 Million Btu/h units.    Products of combustion surplus to the hot oil generator's requirements are discharged    directly to atmosphere; they are not drawn down through the hot oil generator by the 600°F    (315°C) induced draft fan on its discharge. The 1,900°F products of combustion meet 0.05   gr/dscf, 1.5 ppmv and 15 ppmv - for particulate, CO and NOX, respectively - at 12% CO2 by  volume, straight out of the 60 Million Btu/h combustors.

3. Direct fire rotary dryers in panelboard mills

The 2,000°F (1100°C) products of combustion of 45% moisture content (wet basis) wood   residue from a 45 Million Btu/h unit direct-firing a rotary dryer in a NB waferboard plant. Note the wafers falling from the rotary air lock at the top of the dryer down into the 2,000°F gas stream.

Working with other firms, HEI also supplies systems that recover heat and power from the EnvirOcycler's products of combustion.   Two basic Combined Heat and Power Systems (CHP) supplied are:

EnvirOcyclers "direct firing" nominal 1,850°F (1000°C) Waste Heat Boilers (WHB)  (also called  Heat Recovery Steam Generators - HRSG) in “pure”  power plants or in co-generation plants. (see  Figure   7   below  - click  on  drawing  to view enlarged image) 

A “pure” steam power plant is one which only generates electric power. High pressure steam from its WHB is expanded - across a condensing steam turbine driving a generator  -  all the way down to a vacuum of typically 3" Hg.

A co-generation plant is a true CHP. It generates both power and process steam for heating. High pressure steam from its WHB is  expanded down to only between 150 and 300 psia across the back pressure steam turbine that drives the generator.   Process steam from the turbine discharge is routed to one or more sections of the plant for process heating.

EnvirOcyclers "indirectly firing" (via heat exchangers) gas turbine generator sets in the nominal 2 to 10 MWe range.   (See figure 8 below - click on drawing to view enlarged image)

Because the temperature of gas turbine exhaust is typically in the 800°F to 1,000°F range (430°C to 540°C), a WHB is also supplied to recover additional energy in the form of process steam. The WHB is fuelled by the exhausts from both the gas turbine (air) and the heat exchanger ("spent" EnvirOcycler products of combustion).

The presence of the WHB suggests "combined cycle" (a gas turbine followed by a steam turbine) power generation.  While the main purpose of the WHB is to generate process heat - for example, low pressure steam to heat lumber dry kilns - the WHB can produce modest pressure steam which can then be used to drive a moderately sized condensing steam turbine and produce additional power.

HEI also supplies EnvirOcyclers to "externally co-fire" existing fossil fuel burning boilers - typically large, utility, coal burning boilers - with wood or other biomass. The woody biomass reduces the amount of fossil fuel burned in the boiler.  It also earns the utility "CO2 credits".

The term "externally co-fire" is used herein, as opposed to the more common term "co-fire", to draw the distinction between burning wet or dry biomass in stand-alone combustors, external to the boiler, and burning a mixture of dry biomass and coal in the boiler's coal burners. In the "external co-fire" case 99+% of the biomass ash does not enter the boiler; it stays in the external combustor from which it is removed by the built-in ash removal system; in the "co-fire" case the ash enters the boiler.

The impetus for "co-firing" is the 1997 Kyoto agreement to limit green house gases (GHG's) world-wide.  Kyoto  was followed up with President Clinton's August 1999 Executive Order to triple the use of bioenergy and bioproducts by 2010 in the US.   

CO2 from the burning of fossil fuels is considered to be a GHG. However, CO2 from the burning of biomass is not considered to be a GHG.  The argument is made that, because trees and plants naturally release CO2 when they die - which is immediately absorbed by nearby growing trees and plants - the CO2 released when wood is burned is similarly absorbed and the net effect on the atmosphere's GHG load is zero.

The HEI approach is to "externally co-fire" these boilers with the 2,200°F (1200°C) products of combustion of biomass of varying moisture and ash contents.  See Figures 9 and 10. 

One or more EnvirOcyclers are installed within 100 or so feet (30 m) of the boiler and their products of combustion are ducted (in refractory-lined breechings) into the bottom of the boiler, just below the pc burners.  The existing coal pulverizing/feeding system is untouched. The cost of a typical external co-firing system comprising one or more EnvirOcyclers and a  fuel storage/handling system is about US $300/kWe. 

As an example, to displace 10% of the coal burned in a 270 MWe utility boiler costs
                   0.1 * 270,000 kWe * $300/kWe
                     or just over US $8 Million. 
Three 75 Million Btu/h EnvirOcyclers are required.

Fig. 9 Click on drawing to enlarge view

Fig.10 Click on drawing to enlarge view

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