ANSALDO CALDAIE - Steam Generators and Clean Combustion Systems

With more than 1,000 units worth about 80GWe capacity installed around the world, ANSALDO CALDAIE is the most experienced Italian designer and manufacturer of steam generators. Over the years we have blended our knowledge with the expertise of BREDA Termomeccanica and FRANCO TOSI, the other two historical Italian boilermakers.

We design and supply high quality steam generators and clean combustion systems utilised in power generation and environmental applications. These include in-furnace NOx emission reduction systems, coal, gas and oil fired utility boilers – with sub-critical and supercritical parameters – up to 660MWe, HRSG downstream gas turbines up to 260MWe, waste heat boilers for municipal and industrial incinerations and industrial boilers.

Furthermore, we have experience in burning alternative fuels such as Orimulsion®, Biomass, RDF. Our product development is validated by the tests we make in our state-of-the-art combustion and environment research centre equipped with a 50MWth combustion test rig and a 6MWth re-burning simulation facility.

IN-FURNACE NOx EMISSION REDUCTION SYSTEMS

We offer a structured approach that, depending on the NOx emission requirements set by customers and the environment regulations of the user's nation, may result in the use of:

• Low-NOx burners TEA-C (firing coal and oil) and TEA-BA (firing oil and gas)
• Air staging (over fire air or two stage combustion) and its simplified forms - closed coupled OFA and burners out of service
• Fuel staging (reburning or three stage combustion)
• Flue Gas Mixing (GM) and/or Flue Gas Recirculation (GR).

Sometimes, we offer a stand-alone solution (e.g. in case of low NOx burners), more often, a combination.

LOW NOx BURNERS (LNB)

TEA-BA fires oil and gas. In most cases, due to its limited size and low-pressure drop, this burner can fit into existing burner throats, thus reducing retrofit costs and boiler outages. Its specific design allows very low excess air operation and optimised coupling with staged combustion. NOx reduction averages 50% in respect of originally installed (non low NOx) burners.

TEA-C fires coal and oil. This burner has proven capable of attaining NOx emission in coal firing of 550mg/Nm³ ÷ 650mg/Nm³ @ 6% O₂ with full control of UBC (4% to 6%). It is plant qualified for optimised use in staged (OFA / Reburn) combustion schemes.

AIR STAGING

Conventionally known as Over Fired Air (OFA) technique, Air Staging involves diversion of 20% to 30% of combustion air from main burners to injection nozzles located in the upper part of the furnace, in order to produce sub-stoichiometric conditions in the primary (fuel injection) zone and consequently to depress NOx formation.

The quick and uniform mixing of OFA flow, which is a key issue for the successful application of this technology, is optimised by the competant use of "in house" developed and field validated CFD models. LNB + OFA can provide, in retrofit applications, NOx reduction of 65% to 75%.

REBURNING

This technology has been developed to maximize the "in-furnace" NOx emission reduction and requires part of the total fuel heat input to be injected into the furnace in a region above the primary (main burners) flames to create a reducing atmosphere (re-burn zone), where hydrocarbon radicals react with NOx to produce elemental nitrogen.

To assist the efficient mixing of reburn fuel with the upcoming products of combustion, a proper flue gas flow from economiser outlet is recycled and injected into the furnace with the reburn fuel. An OFA flow is then injected above the reburn zone, to secure the complete combustion of unreacted hydrocarbons.

Overall NOx reduction in the range of 75% to 85% can be achieved by optimising the injection system design and the process performance.

UTILITY BOILERS

Box type boilers up to 320MWe include the following features:

• Compact design with two gas passes above the furnace
• Sub-critical parameters
• Suitable for gas and oil firing
• Membrane wall construction
• S/H, R/H and economiser fully drainable

Two-pass type boilers up to 600MWe include the following features:

• Coal, gas and oil firing
• Sub-critical parameters
• Fully drainable

Once through type boilers up to 660MWe include the following features:

• Benson technology
• Coal firing
• Supercritical parameters

HRSG DOWNSTREAM GAS TURBINES UP TO 260 MWE

Horizontal type includes the following features:

• Horizontal gas flow, natural circulation
• One to three pressure levels, with or without reheat
• Top supported pressure elements
• Cold casing
• With or without supplemental firing and/or forced draft fan mode (fresh air)

Vertical type includes the following features:

• Vertical gas flow, assisted circulation
• One to three pressure levels, with or without reheat
• Top supported pressure elements
• With or without supplemental firing

WASTE HEAT BOILERS FOR INCINERATION

Main features include:

• Furnace with three vertical flue gas passes
• Furnace inner protection by INCONEL cladding
• Convective pass with superheating and economiser
• Auxiliary burners
• Fly and heavy ash extraction system