210MMBtu (61.5 MWth) Renewable Energy from Cellulosic Ethanol Co-products

Outotec’s Advanced Staged Gasifier converts cellulosic ethanol co-products into energy for a second generation renewable fuel plant.

Outotec’s Advanced Staged Gasifier is generating 61.5 MWth of renewable energy for a world-class cellulosic ethanol producer in the state of Iowa, USA.

The ethanol plant processes 770 short tons per day of ethanol co-products, biogas, and corn stover (corn cobs, leaves, husk and stalk) to produce 20 million gallons of cellulosic ethanol per year (later ramping up to 25 million gallons per year).

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

This boiler produces 175,000 lbs/hr (79.4 tonnes/hr) of saturated steam, which is used locally in the cellulosic ethanol production process – helping maximize the economic returns for the plant.

Summary

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Location
USA
Delivery year
2014
Technology
Advanced Staged Gasifier
Commodity
Biomass
Scope
EP

Challenge

  • High fuel moisture content
  • High fuel alkaline content
  • 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
  • Reduced slagging potential due to low operating temperatures

The fuel metering system delivers ethanol wet-cake, biogas and other co-products to the Advanced Staged Gasifier via an airswept stoker into the vessel, which is based on Outotec´s Bubbling Fluidized Bed technology

Initial heat for starting up the renewable energy system is provided by startup burners fired with natural gas. 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, then gasifies at a low, controlled temperature, helping prevent ash from the fuel from melting and coating the boiler tubes. Limestone is also added into the bed in order to improve ash eutectics and capture oxides of sulfur (SOx)

The producer-gas rises above the bed and oxidizes, releasing 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 automatically during normal operation via Outotec’s proprietary bed material cleaning, handling, and storage system.

Flue gas cleanup is completed via dry sorbent injection into the flue gas which then enters a pulse-jet fabric filter baghouse. Any remaining particulate matter is removed from the flue gas with 99% efficiency in the baghouse, after which, an ID 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, manufacture and supply of the advanced stage gasification system from the metering bin to the stack.

Outotec also supplied the startup support and operator training assistance.

BFB Plant facts:

Fuel consumption: 700 tons/day
Fuel mix: Wet cake
  Biogas
  Co-products
Steam parameters  
Flow: 175,000 lb/hr [ 22 kg/s]
Temperature: 405 F [208 C]
Pressure: 255 psig [17 bara]
Air quality control system  
Limestone injection for SOx removal  
Selective non-catalytic reduction (SNCR) NOx  
abatement system  
Dry sorbent injection  
Pulse-jet fabric filter  
Footprint: 87 ft. x 267 ft.

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