The Ecotube System

Ecotube Air Staging :

Ecotubes are strategically positioned inside the boiler in order to radically improve furnace gas mixing and thereby significantly reducing laminar flows. Flue gases will be more evenly distributed over the cross sections of the furnace thus using the available furnace volume more effectively.

Columns of laminar flows from boilers is a well-known fact. The negative consequences with laminar flows, resulting from poor mixing of combustion gases, are fluctuating concentrations of various combustion parameters, short residence times, high particulate carry over and erosion related water wall and super heater problems.

Ecotubes will reduce local high furnace temperatures as well as local high flue gas velocities by adding much needed kinetic mixing energy. Ecotubes will enable the boiler to be operated at a lower O2 level due to improved mixing and flow pattern changes. Lowering the O2 level will reduce carry-over from the bed, increase flue gas residence time and reduce formation of NOx and CO. A lower stoichometric ratio will reduce ware from erosion and corrosion on all effected boiler system systems ultimately leading to longer operation lifetime and efficiency of e.g a lime scrubber, baghouse filter and FD/ID fans. We have documented up to 30% in reduction of fly ash and carry over from the combustion bed when reducing total O2 levels.

CO Reduction Examples
Ecotubes have been installed on several boilers types ranging from Spreader Stokers, Grate Fired Boiler to pure burner boilers burning everything from household waste, biomass and coal.

The following examples of possible CO reductions are from a spreader stoker boiler burning wood waste. The CO reduction enables the Ecotube System to operate the boiler at lower O2 and therefore levels of NOx will be reduced.

Without Ecotube System in Operation (35MWel)



With Ecotube System in Operation (35MWel)



Boiler Load and Efficiency

By optimizing the combustion process the Ecotube System enables to boiler to operate with higher boiler efficiency and reduced emissions of CO2. An optimized final combustion zone results in most cases that the boiler load can be increased while still complying with emission limits.

Ecotube SNCR

The ability of the Ecotube system to reduce NOx formation from the Staged Combustion step can further be improved by adding a NOx reagent such as Urea or Ammonia. These reagents can be added either as solids, liquids or in gaseous form. By adding a reagent via an Ecotube from multiple injection points we are able to reach higher reduction levels with less reagent compared to traditional SNCR systems. The main reason for this improvement in performance is that the Ecotubes add and MIX the reagent where it is needed and not from the boiler walls.

This effect is even more apparent in larger boilers where traditional SNCR systems simply cannot penetrate deep enough in time for NOx reduction to occur. The Ecotube System installation in the CPCU plant in Paris reduced urea consumption from 550 l/h to 150 l/h compared to former traditional SNCR system that it replaced. The two coal fired boilers in Paris are approximately 10*10m (32ft) which makes high NOx reduction rates hard to achieve due to poor penetration and insufficient mixing of the reagent.

NOx reduction performance was also improved in combination with lower reagent usage from 250 mg/Nm3 at 6% O2 to well below 150 mg/Nm3. The ability to use less reagent compared to traditional SNCR systems lowers client reagent costs plus the risk of ammonia slip in the stack is reduced.

Each Ecotube can be equipped with 4 different rows of injection nozzles that each can operated independently or in combination. This gives the Ecotubes the advantage of being able to add the reagent in 4 different directions depending on combustion conditions and boiler load.

Ecotube FGR

Flue Gas Recirculation

An installation of an Ecotube System can be when needed to reach a guaranteed NOx level be complemented with an installation of recirculated flue gas (FGR).

FGR in short, involves returning a calculated portion of the flue gases back into the boiler. The recirculated flue gases can be used as part of the primary air, secondary air or as part of the Ecotube System air. By returning flue gases back to the combustion process a NOx reduction of 15-40% can be achieved. The NOx reduction comes from lowering the combustion temperature and by reducing available O2 needed in the formation of NOx.

A common and known problem with traditional FGR installation is that it will result in a lower furnace temperature and can result in increased CO emissions. With the Ecotube Systems improved mixing capabilities we are able to meet increased emission of CO.

Traditional SNCR

ECOMB AB have designed and installed traditional type SNCR systems using both Urea and Ammonia in liquid form. Traditional SNCR is when the reduction agent is added to the combustion process from the boiler walls via special injectors or in combination with secondary/tertiary air.
This solution is selected when the client has a smaller type boiler where sufficient mixing and NOx reduction rates can be obtained. Depending on the boiler size and layout the injection nozzles are installed at different elevations and reagent flow is adjusted according to online temperature measurements and a NOx Setpoint.