53.5 MWe Renewable Energy Power Plant

Outotec’s Advanced Staged Gasifier converts green wood and wood waste into clean, sustainable, electric power.

Piedmont Green Power uses the Outotec Advanced Staged Gasifier to generate 53.5 MWe net of clean, renewable power for the state of Georgia.

The power plant is fueled by approximately 500,000 tons per year of woody biomass, which is sourced from urban wood waste, logging and mill residuals. Outotec provided the boiler island equipment solution, complete from metering bin to stack.

Due to the inherently high thermal inertia of the fluidized-bed, the Outotec Advanced Staged Gasifier system is well suited to these types of high-moisture-content fuels.

This boiler produces 482,000 lbs/hr [219 tonnes/hr] of superheated steam, which is used to generate electric power under a power purchase agreement (PPA) with Georgia Power, a subsidiary of Southern Company.

Summary

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Customer
Piedmont Green Power
Location
USA
Delivery year
2013
Technology
Advanced Staged Gasifier
Commodity
Biomass
Scope
EP

Challenge

  • High fuel moisture content
  • High efficiency
  • Strict emissions limits

Solution

  • Outotec Advanced Staged Gasifier boiler island
  • Supplied to the client as a “metering bin-to-stack” solution

Benefits

  • Stable operation with varying fuel quality
  • No additional fuel drying needed before combustion
  • Low emissions due to inherent properties of the bubbling fluidized bed

Clean urban forestry and mill waste is delivered to the Piedmont Green facility via truck. The trucks are scaled, then loads are dumped via drive-through, tilt-up dumping stations. Metal is removed from the wood via magnetic separators. The material continues to a screening system which sorts the material to three inches or less, while oversized material is routed to a hammer mill for size reduction. The screened and sized material then travels by conveyor to the fuel yard and is sorted into piles by an automated stacker / reclaimer system.

Fuel from yard is conveyed to the fuel metering bins, which maintain enough fuel for eight (8) minutes of operation. The fuel metering bins deliver the fuel via an air-swept stoker into the Advanced Staged Gasification vessel, which is based on Outotec’s fluidized bed technology.

Initial heat for starting up the renewable energy system is provided by overbed and underbed burners fired by biodiesel. A steam coil air heater provides warmed air to the inlet of a 900 HP forced draft (FD) fan. Air from the FD fan fluidizes the bed media such that it bubbles like a boiling pot of water. Fuel entering this hot, bubbling bed area, first releases its moisture, and subsequently gasifies into producer-gas in a sub-stoichiometric environment.

The producer-gas rises above the bed and is fired above the bed to release its thermal energy. NOx abatement occurs inside the main vessel’s upper vapor space via nozzles that spray ammonia into the flue gas, which then reacts with nitrous oxides to form nitrogen, carbon-dioxide and water.

Any remaining, inert fuel contaminants, such as metal or rock are removed from the bed continuously during normal operation via Outotec’s proprietary bed material cleaning, handling, and storage system.

Energy is recovered from the sensible heat produced via a boiler design proprietary to Outotec. Any remaining energy that cannot be utilized for steam production is recovered in the economizer, which pre-heats the incoming water to the boiler.

Flue gas cleanup is accomplished via dry sorbent injection into the flue gas which then enters a pulse-jet fabric filter baghouse. Over 99% of the particulate matter is removed from the flue gas in the baghouse, after which, an induced draft fan pulls clean flue gas from the baghouse and disperses it via the stack. Emissions are monitored via a continuous emissions monitoring system (CEMS) which measures carbon monoxide, oxygen, nitrogen oxides, sulfur dioxides, and opacity

Scope of Supply:

Outotec´s EP scope included the design, manufacturing and supply of the advanced staged gasification system from the metering bin to the stack. Outotec supplied also the startup support and operator training assistance.

BFB Plant facts:

Fuel consumption: ≈1500 tons/day [1364 tonnes/day]
Fuel mix: Green wood + wood waste
Steam parameters:  
Flow: 482,000 lb/hr [219 tonnes/hr]
Temperature: 1005 °F [541°C]
Pressure: 1515 psia [104.5 bara]
Air quality control system:  
Selective non-catalytic reduction (SNCR) NOx abatement system  
Dry sorbent injection  
Pulse-jet fabric filter  
Continuous emissions monitoring system (CEMS): CO, O2, NOx, SOx, Opacity

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