Waste-to-Energy

Keppel Seghers AIR-COOLED GRATE | Keppel Seghers WATER-COOLED GRATE
Keppel Seghers BOILER | Keppel Seghers PRISM | Keppel Seghers GRATE SERVICING
Keppel Seghers COMBUSTION CONTROL SYSTEM

Applications
The Keppel Seghers AIR-COOLED GRATE is perfectly suited for small to high capacities (1.5 tonnes per hour up to 30 tonnes per hour) and for low to moderate calorific waste-to-power incineration(6,000 to 14,000 kJ/kg).

The unique concept of independent horizontal movement (transportation of the waste through the furnace) and vertical movement (poking with the tumbling tiles) allows the Keppel Seghers AIR-COOLED GRATE to adapt effortlessly to short and long term fluctuations in domestic waste composition.

Advantages
The Keppel Seghers AIR-COOLED GRATE for waste-to-energy installations:

• demands minimal construction time thanks to prefabrication and modular structure,
  
• offers very high operating flexibility by its unique concept of independent vertical and horizontal movement of the tiles,
  
• incorporates excellent combustion control by an optimised and independent primary air supply to each grate element,
  
• passes primary combustion air through horizontal openings rather than vertical ones, thus reducing loss of ashes through grate siftings,
  
• is characterised by a high durability of the tiles, guaranteed due to the use of high-quality refractory cast steel, the absence of friction between tiles in the same line and the absence of friction between adjacent rows of tiles thanks to scrapers.

Description
Despite various attempts by governments to prevent waste production, the amounts of municipal waste are still burgeoning. Therefore, a sustainable development approach requires that the concept of "waste" is replaced by a concept of waste as a "resource". This explains that a modern Waste-to-Energy plant forms an integral part of good waste management.

The Keppel Seghers AIR-COOLED GRATE is ideally suited for use in installations for thermal treatment of various kinds of municipal and industrial waste having low to middle calorific values. The combustion grate serves as a carrier for the horizontal combustion processes. All different reaction zones (drying zone, degasification zone, combustion zone, burn-out) of the combustion process need specific operation conditions. For example: for the drying process a lot of oxygen is necessary, so in that area it is important to increase the frequency of the poking movement (tumbling tiles).

The Keppel Seghers AIR-COOLED GRATE is the only combustion grate which incorporates separate and independently controlled actuators for waste transport and waste mixing. This results in a better control of each reaction process and a more complete combustion of the waste.

• Sliding tiles gradually push the refuse layer on the grate forward, hence establishing a slow and continuous movement. This movement determines the furnace throughput, the thickness of the refuse layer on the grate, the residence time and the combustion quality.
• Tumbling tiles disentangle and aerate the refuse, resulting in thorough mixing. This action is essential for drying and igniting the refuse, initiating combustion and assuring a complete burn-out in case of low caloric waste.

Applications
The Keppel Seghers WATER-COOLED GRATE is perfectly suited for high flexibilities in waste composition and for high calorific waste (10,000 to 30,000 kJ/kg).

Advantages
For combustion of high calorific waste, the Keppel Seghers WATER-COOLED GRATE technology is highly recommended.

• Thermal peaks as a fact of changing calorific values are absorbed through the cooling system because of localised cooling.
• Since the cooling function is completely independent from the supply of combustion air, the amount of primary air can be selected in function of the combustion process. This allows a lower air excess in the furnace and increases the efficiency of the boiler.
• The tiles are constantly kept at a lower temperature, which substantially increases their lifetime. Operation of about 32.000 hours and more with less than 10% replacement is possible.
• Thanks to the special concept of the water cooled tile, the tile width is increased, resulting in a limited number of connections for the water cooling circuit, thus limiting the risk of leakage;
• Throughput of dust and slag through the grate steps is negligible because of minimum space between grate tiles. The additional advantage of the absence of space between the grate tiles is that the primary air is forced through the air openings in the tiles ensuring a stable homogeneous flame front and a better burnout.
• The concept can easily be used for upgrade of already existing combustion grates when the calorific value of the waste has increased.

Description
There are two types of row tiles :

• Sliding rows with tiles making the horizontal movement : these rows move forward and backward horizontally in unison, thus ensuring that the burning waste layer is transported horizontally.
• Fixed rows.

The side walls of the grate and tiles are provided with water cooling. The tile body and head are drilled with a sufficient number of holes, where the cooling water is forced through in a serpentine line. The high width of each tile minimises the number of connections in the water cooling circuit.

The cooling circuit of the tiles exists of a circuit of drilled canals in the tile body material. The absence of leaks is tested at a pressure of 50 bar. The combination of the integrated cooling canals and the high pressure resistance makes a grate operation with a cooling water temperature of 105 ° C possible.

The high velocity in the water cooling circuit prevents the formation of air bubbles. The water circulation in the tiles and sidewalls maintains the water temperature below 100°C and avoids formation of steam.

Each grate row can be isolated by means of valves, so that revision on a singular grate row can be executed during operation of the plant and without shutting down the cooling of the other grate rows.

Applications
The Keppel Seghers BOILER is the ideal solution for optimal heat recovery in waste combustion plants. It is the key component in the energy recovery process and more general in the combustion process for several reasons:

• Transfer of heat from flue gases into steam.
• Part of the combustion takes place in the boiler.
• Part of the flue gas cleaning takes place in the boiler.

Advantages
Extra income due to the selling of steam and/or electricity.
No increase of flue gas flow compared to cooling with cold air or with water (cooling tower), requiring smaller flue gas cleaning necessities.

Integrated system, consisting of an combustion chamber and a heat recovery system.

Description
Only a portion of the combustion process takes place on the grate while an important part occurs in the boiler, making an integrated approach essential. During the design and engineering stage, intensive use is made of two- and three-dimensional numerical simulations (CFD-calculations) to optimise the furnace and boiler geometry with respect to the flue gas flow pattern, the combustion air distribution, the dust removal and the heat transfer.

The Keppel Seghers BOILER can be subdivided into two different parts:

• A radiation section where the heat is basically transferred by radiation, which is located in the high temperature range (1200 - 650°C). In this section the boiler is built up of water-cooled walls, thus no tubes are installed in the flue gas flow and this section is therefore called the "empty passes".
• A convection section where the heat is basically transferred by convection, which is located in the lower temperature range (650 - 200°C). In this section the boiler is built up of water-cooled walls in which lots of tubes are hung in the flue gas flow. The tubes are arranged into different blocs with each its own function.

The reason for the existence of two different parts: being the "empty passes" on one hand and the "convection section" on the other hand is a result of the aggressive nature of the flue gases. In the convection section the boiler tubes are directly into contact with the flue gases (hung up in the flue gas stream). The combination of some pollutants and the temperature results in a high risk for corrosion of the boiler tubes. Therefore the flue gas temperature is reduced up to about 650°C (in the empty passes) before coming into contact with the tubes of the convection section.

Applications
The Keppel Seghers PRISM is perfectly suited for optimised secondary air injection of Waste-to-Energy plants having a high capacity. The application is not restricted to new installations. The boiler prism can also be installed in existing Waste-to-Energy plants.

Advantages

• optimal secondary air control
• reduction of boiler fouling due to a more homogeneous post-combustion and absence of hot spots
• increase of operation time without mechanical cleaning of the boiler
• increase of plant availability
• lower ammonia consumption for the SNCR installation (if any)
• less fly ashes in the boiler due to less primary air flow
• less corrosion at boiler heat exchanging surfaces

Description
The Keppel Seghers PRISM technology constitutes a novel and innovative means of increasing combustion and boiler performance, based on the invention of a prism-shaped body in the first empty boiler pass. The prism allows a highly optimised secondary air injection and combustion control strategy leading to more homogeneous flue gas conditions at a very early stage and virtually independent of the heat release profile on the grate. This not only leads to increased performance in new boilers, but also helps to solve the severe corrosion problems in the radiant and superheater sections that many existing plants are suffering from.

The improvements on the combustion and post-combustion processes with this new secondary air injection system result in a much shorter and clearly defined burn-out of the flue gases just above the prism.

The flue gas temperature measurements in the passages next to the prism not only regulate the secondary air injection, but also control the air distribution under the grate.

Applications
The Keppel Seghers COMBUSTION CONTROL SYSTEM is specifically designed for optimal operation of Waste-to-Energy installations. The control system forms the brains behind the combustion process. It allows operators to receive direct feedback in order to preserve the efficiency and uniformity of the entire operation.

Advantages
The Keppel Seghers COMBUSTION CONTROL SYSTEM optimises the combustion process by maintaining:

• constant and minimum discharge of flue gases, with a constant oxygen content ;
• good quality slag ;
• maximum control throughout;
• maximum energy production.

Description
The concept integrates two principles, depending on the heating value of the waste. Transition between both happens automatically.

• Operation at nominal thermal load
  When waste with a higher heating value is burnt, the main purpose of the operation is to generate a constant steam flow. In this situation, the boiler reaches its nominal thermal load.
• Operation at nominal mechanical load

When waste with a lower heating value is burnt, the main purpose of the operation is to achieve the nominal waste throughput.

The components of the Keppel Seghers COMBUSTION CONTROL SYSTEM can be divided into the following categories:

• the instruments;
• the actuators (e.g. the hydraulic cylinders, the frequency controlled drives of each fan, …);
• the controllers (e.g. oxygen, steam, air resistance,…).

Applications
Revamping / upgrading of:

• Feeding hopper, including valve and drive
• Feeding grate
• Tiles of combustion grate (supply of new combustion tiles, revamping an air-cooled grate towards a water-cooled grate)
• Support structure and drive of combustion grate
• Side walls (expansion, water cooling, …)
• Slag chute
• Deslagger (wet deslagger, dry deslagger,…)
• Boiler (prism,…)

Advantages

• Higher performance of existing combustion plants
• Meet more stringent emission limits
• Extented operational lifetime of the installation

Description
Operating a furnace/boiler for solid waste combustion successfully calls for professional maintenance and continuous improvement of different components. Disruptions due to expensive, unplanned repairs or poorly prepared shutdowns can result in runaway cost. With its expertise, Keppel Seghers can help improving the availability and reliability of different types of grate combustion plants.

Upgrading of components includes dismantling, modification, assembly and commissioning in addition to site management.