Escalante Generating Station, Prewitt, NM

Station

Escalante Generating Station #1

Nominal Size

250 MWe

Boiler Type

Tangentially fired with 5 levels

Fuel

Waste paper sludge / subbit coal

Max cofiring %

1% wt

Duration

2 years

Fuel Preparation

Blended

Power Plant Description:

The Escalante Generating Station is located in Prewitt, NM, twenty-seven miles northwest of Grant, NM in the heart of the uranium mining area about 105 miles west of Albuquerque.  The plant was recently acquired by Tri-State Generating & Transmission Association, Inc. from the Plains Electric G&T Cooperative. There is one boiler at the plant.

Boiler #1 is a 250 MWe tangentially-fired pulverized coal boiler built by Combustion Engineering in 1984.  It operates at 1800 psig 1000oF and 1,800,000 #/hr steam flow.  The boiler burns New Mexico subbituminous coal at about 9,000 Btu/lb.  There are five pulverisers on the unit which delivers pulverized coal to five levels of the boiler at the four corners.  The boiler has a baghouse for particulate control and a wet limestone scrubber for SO2 control.

Project Description/Objectives:

The personnel at the Escalante Generating Station recently embarked on a program to burn waste paper sludge in their boiler by blending on the coal pile and in the rail receiving area.  They burned the sludge at a rate of about one percent by weight.

The objectives of the testing were to: help out a power customer, improve relations with that customer, pick up or save some revenue, and get involved in “green” power.

Project Design:

In 1998, to help the McKinley Paper Company, the plant tried burning their paper sludge waste.  The paper company is a cardboard recycling mill.  They take OCC (old cardboard containers), chop them up wet, and make new liner board for cardboard cartons.  They generated about 100 wet tons/day of 60% moisture (4,000-5,000 Btu/lb) waste that was too fine to use as cardboard.  The paper company was paying a $23 tipping fee to a landfill 12.5 miles away.  It cost an additional $5/wet ton to transport the sludge to the landfill.

The paper company produces 525 tons of product per day and should generate about 50-55 tons/day of sludge but problems at the facility caused a greater amount of waste than design.  This caused problems at the landfill and the paper mill needed to find other ways to reduce the cost of disposal.

The system at Escalante Station was very basic.  The sludge was brought over by dump truck from the paper company close by and dumped on the top of the coal pile.  It was allowed to sit on the pile to air dry for a couple days and then was blended by dozer on the pile and pushed into the reclaim hopper to the plant.  The sludge was the consistency of damp finely shredded newspaper.  The blend (approximately one percent by weight) then went from the reclaim hopper to the bunker.  This blending method was not very accurate so they subsequently altered the method and delivered the sludge by dump truck to the rail car dumper hopper area and piled it on the ground.  Coal trains were unloaded three times/week.  They would use a high lift to load 50 tons of paper sludge into the hopper with 52 100-ton rail cars of coal.  The blend was then well mixed in the rotary car dumper and stocked out on the coal pile.  Rainfall is very low in this area so rewetting of the paper was not an issue.  They had to get both air and water permits to do the test burns.

Project History/Status:

The first test burns were conducted in 1996 and ended in December, 1997.  They burned approximately 10,000 tons of paper sludge over a two year period.  The analysis of the paper sludge was 60% moisture and 7,184 Btu/lb on a dry basis.  A second series of tests were conducted in January, 1999 and ended in February of that year due to a change in the operations at the paper plant which caused problems in the plant pulverisers.  In order to reduce the amount of waste paper sludge and increase the amount of usable fibers, the paper company began using a polymer in the process.  This polymer in high concentrations caused “rocks” to form in the pulverisers at the plant.  There was no negative effect on the boiler but the problem with the pulverisers could not be resolved.  The paper company tried to design a screw press to alleviate the problem but so far, they have not been able to do so.

Results/Conclusions:

The initial test burns were successful.  There were no operational problems.  At this low level of cofiring, the boiler basically didn’t see the sludge. There was no difference in emissions, load or operation of the scrubber. They sell fly ash at the plant and tested to see if there was any change in the ash. There was no change. The sludge was undetectable. They ran for several months and shut down due to some contractual issues.

When they started up again in 1999, the paper company had changed their formulation and started putting polymer in the sludge to increase fibre recovery. This gummed up the pulverisers as described above. As recently as August, 2000, the paper company and the power plant tried again to burn the sludge. They were not successful. The power plant would burn the paper sludge if the paper company can get the polymer problem behind them but they are not currently burning paper sludge.

Project Partners:

­          Escalante Generating Station personnel

­          Plains Electric G&T Cooperative Corporate R&D

­          Tri-State Generating & Transmission Association, Inc., Corporate R&D

Contacts:

­          Don Russell, (Plant Mgr.), 505-876-5217, drussell@tristategt.org

­          Tri-State Generating & Transmission Association, Inc., 1100 W. 116th Avenue, Westminster, CO 80233, 303-452-6111

­          Escalante Generating Station, PO Box 577, Prewitt, NM 87045, 505-876-2271