Greenidge Generating Station #6, Dresden, New York
Power Plant Description:
Greenidge Generating Station is located on the western shore of Seneca Lake in Dresden, New York. The station was recently acquired by AES from New York State Electric & Gas (NYSEG). There are currently three boilers at the station: #4, #5 and #6.
Boilers #4 and #5 are twin 28 MWe front-fired pulverized coal boilers manufactured in 1950 by Babcock & Wilcox with a steaming capacity of 280,000 lb/hr at 865 psig and 900oF. They each have four burners that are arranged (two over two) on the front wall of the furnace. The boilers are each equipped with an electrostatic precipitator for particulate control and overfire air systems for NOx control. The boilers burn eastern bituminous coal at a full load rate of 14 tons/hour.
Boiler #6 is a 108 MWe tangentially-fired pulverized coal boiler that was manufactured in 1953 by Combustion Engineering. The steaming rate of the boiler is 750,000 lb/hour at 1465 psig and 1005°F. The boiler has four Raymond bowl Model 533 pulverisers. There are sixteen burners on the boiler that are arranged as four elevations of four burners on each corner of the boiler. This boiler is equipped with an electrostatic precipitator for particulate control. Gas reburn was added for NOx control in 1996. This boiler burns eastern bituminous coal at a full load rate of 42 tons/hour.
Greenidge Station has installed a system capable of cofiring wood chips up to 30% by weight in Boiler #6. An average blend of particle board containing 7,800 Btu/lb and little or no moisture is the target cofiring fuel along with small amounts of other wood wastes. The system is run about 16 hrs/day. This equates to about 120 dry tons of sawdust per day at full capacity. The fuel arrives at the plant at about minus 2” in size which is then reduced to minus 1/4” before injection into the boiler. The moisture varies from a low of 10% to a high of about 40% yielding a Btu range of 4,500 to 8,000 Btu/lb. The main objective of the cofiring system was to reduce the cost of fuel burned at the plant and therefore increase its dispatch rate.
The biomass handling system consists of a receiving ground level stockpile where various wood wastes are received by truck and loaded onto an above ground open grate. The wood is then transported by sliding gates to a conveyor which transported the fuel originally to a series of two hammermill-crushers which reduced the overall size of the wood to minus 1/4”. After the crushers, the fuel was blown into the boiler through two separate 6” diameter injectors located at opposite corners of #6 Boiler at about the middle elevation of the coal burners.
The advantages to separate injection are many. Separate injection gives the boiler operator control of the system. If something should go wrong with the blend or, if there is a problem on the boiler, the system can be shut down. There is much greater control of the fuel input at reduced loads. The separate injection also allows much higher percentages of wood versus placing the wood on a belt and feeding it through a pulveriser. At only 5% wood by weight, the pulveriser performance can be adversely affected. The only downside is the initial cost of the separate injection system versus a very low capital expense associated with blending.
Greenidge Station began their wood cofiring program in late October, 1994 using separate injection of the wood into the #6 Boiler. These tests were inspired by the success of cofiring on stoker boilers at other NYSEG sites. Initially the wood was introduced through one idle coal pipe on one pulveriser at a rate of about seven tons/hour. The fuel was blown into the boiler using a 50 hp blower. During parametric testing at 5% by weight, the NOx levels were reduced a small amount and SO2 dropped due to the low sulphur content of the wood. There was little or no effect on opacity. The test results were encouraging and resulted in the station instituting a sustained cofiring of wood near the end of 1997 which continues to this day. They are looking to increase from a two-shift to a three-shift operation in the near future.
A similar program has been implemented at the Seward Generating Station of GPU Genco.
When operating at the maximum wood injection capacity of 30% by weight, the boiler efficiency loss was about 0.8%. There was no reduction in boiler steaming capacity. Particulate levels and CO were unaffected. The SO2 emissions dropped by about 15%. An insignificant decrease of NOx at 0.4 to 0.6 tonnes/day was seen when co-firing a 5% wood energy input with 35% to 45% moisture. For CO2, the replacement of one megawatt of coal-fired generating capacity with biomass results in a reduction of 6,000 tons of CO2/year. Their planned 20% cofiring level by weight, therefore, could offset about 65,000 tons CO2/year.
The plant continues to burn waste wood. In 1999 the #6 Boiler burned over 30,000 tons of wood wastes of various kinds on a two-shift basis without any major problems. On average, this equated to about 15% of the boiler’s total output. Modifications have recently been made to the size reduction system to allow the station to increase its average cofiring capacity to more than 20% by weight and maximize its fuel savings. The original hammermills were operating at more than twice their initial rated capacity of 3 tons/hour. A new single hammermill is rated at 15 tons/hour and should allow greater use of wood.
Greenidge Station Personnel
NYSEG Engineering Department
Dick Bentley, Greenidge Station, AES, 315-536-2359 ext. 211, firstname.lastname@example.org
Carl Radder, Greenidge Station, AES, 315-536-2359 ext. 243, email@example.com
Doug Roll, Greenidge Station, AES, 315-536-2359 ext. 228, firstname.lastname@example.org