Document VGE8zERqp4k1pb3zNRp1Nny0K

1 OPERATING AISLE- The two new 100.000-tb-per-hr boiler* ond stoirwoys, to either the bosament or the drum plotform ond ore crronged so meter ond control panels, feedwater volvcs fan room, ore In or near possagswoy between the two boiler* Steam Plant Modernized With Pulp and paper mill eliminates four old stoker-fired boilers, and superimposes 600-psi 700-F steam and power generators on 170-psi 475-F system. Power-plant design emphasizes reliabil ity, economy, easy operation and provisions for expansion By W P LONDON, H. G. Aero* & Co, Nhgaro Fell*, Ontario Mapcihc pulp amd PAPER consumes large quantities of steam and decide power. Not only are these items es sential to the process, but they also account for a substantial part of the finished product's cost So it is not surprising that successful pulp and paper mills watch boiler-house and power-plant performance with a critical eye while carefully considering all pos sible improvement* in reliability and economy. Thus Fraser Companies Ltd have recently constructed a new steam plant at their mill in Edmunston, N. B., Canada. Existing Plant. When the mill was built before World War l, its steam .and power facilities were adequate end economical. But SO years of con- linuous operation at constantly increas ing production rates had their inevit able result. By 1941, the management realised it could meet present and future needs only by making major additions to the equipment So our firm, H C Acres & Co, undertook a study to determine what equipment to Install (or best economy and reliability --in cooperation with F 0 White, chief engineer for Fraser Companies. Diagram on facing page shows plant hookup in 1941. Pulp-mill steam was supplied st 170 and 25 psi. Boiler installation consisted of eight longi tudinal drum boilers, each of 5000-sqft steam-making surfaces fired by under-feed stokers. Four, equipped with dutch ovens to burn wood refuse. were designed to operate at 170 pal and 475 F. A steam accumulator of 23,000-lb storage capacity was installed between the 170- and 25-psi mains. Two 1000kw extraction-condensing turbine-gen erators had their bleed points connected to the 25-psi system. These supple mented tire main supply of hydroelec tric power. Two 2000-kw electric boilers supplied 170-psi steam when surplus hydro power wss available. Proposed Changes. The steam and power study resulted in a decision to modernize the plant in two'steps: I. Install two new 100,000-lb-por-hr steam generators, bach designed lor 000 psi, 700 F. They could supply full mill requirements but no spare capa* city. These units, with auxiliaries and feedwater-treating equipment, were to be houaed in an extension to the old plant so they could be installed with out interfering with operation. Pro vision was made for a possible- exten sion for two additional units., The final installation could deliver 300,000 lb of steam per hr, with one unit as a spare. This was regarded as the ulti mate plant capacity. Temporarily the now units would operate at 170 psi and connect into the old piping aystem. 2 OLD PLANT ARRANGEMENT. Steam lor pulp mill wot having 5000 sq ft of heating surface, all stoker fired; 4 supplied at 170 psi from eight longitudinal boilers, each ere equipped with dutchoven fumoce* to burn wood rofuto Eye Toward Future Expansion 2. Remove four old boilers and in stall a 3500-kw turbine-generator in their place. This work would not be undertaken until the now boilers had operated long enough to make all ad justments so further shutdowns would be unlikely. 'The Tour old units with dutch-oven furnaces would serve as spare capacity for the now plant and permit using any wood refuse 8S fuel, (t was not desirable to install new refuse-burning units as it was hoped that, by the time the Installation had to be abandoned, more advanced de signs would be available. The turbine-generator was designed lor inlet conditions of 600 psi, 700 F and for 170-psi exhaust It would not develop the total power available from process steam, and space was provided for a second unit of equal capacity. Installing the new power-generating unit in the old building not only ef fected a considerable saving but also 8#ve a more compact and convenient layout. Diagram on p 67 shows final hookup. When the decision was made to pro ceed, material was not available so instruction did not start until 1944. t In 1945 the boiler house wn com pleted and the new boilers pieced in operation. The turbine-generator was placed In service in July 1947. Steam-Generating Unit*. Boilers have an actual capacity of 87,000 lb per hr each, at 620 psi at the superheater out let and a total temperature of 700 F. Pulvcrized-fuel firing is used, designed for bituminous coal from the Minlo area in New Brunswick; overage proxi mate analysis is volatile matter 27%, fixed carbon 40%, ash 23% and mois ture 10%. Its ash softens at 1900 F, has a grindability of 70 and 10,500 Btu as fired. Sulphur content is gen erally high. These characteristics were considered in the firing.equipment de sign. Each boiler has aroplo ..pulverizer capacity In two bowl-type units of 7000-lb-per-hr rating. To insure dry ing the wet'cool, preheated primary air is mixed with a quantity of hot gas drawn from the furnace below the water-cooled ash screen. This get sup plies sufficient heat to permit complete drying under all conditions and to maintain a uniform temperature of the coal-air mixture going to the burners. These pulverizers have been highly satisfactory. Pulverization is excellent and, even with coal of very high ash content, carbon lots in the refuse is extremely low. All grades of coal are handled without difficulty with low mill- maintenance cost. To guard against slagging, liberal furnace volumes and furnace-heat-ab- sorbing surface are provided. At full lood, heat release la about 23,600 Btu par cu ft and 80,000 Btu per sq ft of projected watercooled surface. Water- cooled surface has fin tubes on tbe sidewalls and roof with plain tubes and e refractory backing in the front wall. Experience shows tho units can operate continuously at rated capacity, with about 30% excess air, without serious slagging. '* Each boiler has a plate-type air heater. The coal's flue gas is likely to be corrosive because of high sulphur content, so low gas temperature mast be avoided. At full load, exit-gas tem perature U about 380 F and correspond ing air temperature ebout 420 F. Induced-draft fans are motor driven through hydraulic couplings for speed control. Forced-draft fans are also motor driven and have inlet-vane con trol. Multi-element tubular dust col lectors are installed between air heat ers and induced-draft fans. Coot Handling. Coal is delivered by railway. For the old plant, a track fOWER . July 1946 (369| 4S