The Tail gas generated during the carbon black production has a significant energy content due to its high proportion of combustible elements.
For environmental reasons the gas has to be treated in a thermal oxidizer process to minimize the quantity of hazardous substances. It is profitable to make use of this thermal energy to produce steam or electricity.
Tail gas Boilers have proven themselves in practice in the carbon black industry all over the globe. Combined with Tail gas Combustion a system results which particularly meets the high requirements of the carbon black industry in terms of availability, maintainability, efficiency, and environmental protection.
Advanced tail gas boilers are of modular designs, taking into account individual requirements. The basis is the Combustion Chamber and the Heat Recovery Boiler.
Due to low amount of CO, the heating value of the Off gas is low compared to conventional fuels like Oil and Gas. This results in low adiabatic combustion temperatures (1300 DegC) whereas those of Oil and Gas are high (2000 DegC). The low calorific value gas needs a longer time to burn and produces an unstable flame. This shows obviously that the conventional methods used for Oil / Gas Combustion systems with membrane wall Boiler cannot be applied to Off gas. During the combustion of Off gas in direct-fired conventional membrane wall boiler, the combustion temperature is further reduced by the flame radiation (transfer of heat) to the Boiler Wall. Due to this reason, a complete combustion is not possible. Our solution to this problem is “Convection Boiler” with external, refractory-lined Reaction Furnace, which avoids any flame or fuel gas radiation (heat transfer) to the Boiler surfaces before fully oxidizing / combustion is completed. Due to low amount of CO, the heating value of the Off gas is low resulting in low adiabatic combustion temperatures. The low calorific value gas needs a longer time to burn. For combustion of low-calorific-value fuels the following are very important :
Our Off-gas combustion Furnaces are built to incorporate these three requirements. The combustor-a refractory-lined Furnace is kept hot to provide the proper temperature, cyclonic principle is used to provide the turbulence and intimate mixing of the Off gas and combustion air, adequate combustor volume is provided for the necessary residence time to complete the oxidation of the combustible components.
MTPL Product Development team has vast experience in successful execution many Tail Gas Boilers for the Carbon Black Industry in India and Overseas with other leading tail gas boiler manufacturer in India. We can offer Tail gas Fired Boilers up to 150 tph.
MTPL design of Carbon Black Gas Boilers is suitable for turn-down ratio of 25% to 110% of MCR without support fuel. Hence, better flexibility and fuel savings.
MTPL design of Carbon Black Gas Boilers do not require support fuel till the BF gas flow comes below 25% of MCR or LHV fall below 450 Kcal/Nm³.
In our design of Carbon Black Gas Boilers, the combustion is controlled by sensing the fuel gas temperature (more reliable) compared to Flame Scanner, when temperature of fuel gases fall below 850°C due to BF gas flow below 25% of MCR, or LHV of gas falls below 450 Kcal/Nm³, support fuel cuts-in automatically, to sustain the combustion / heat release, avoid trip and maintain Steam Generation Rate. This arrangement ensures smooth and steady operation and avoids a trip.
Waste gases emanating from the sponge iron kilns exiting the post combustion chamber at about 900 – 950 DegC are used to generate steam in a waste heat recovery boiler (WHRB). The steam so generated is used to produce electricity in Steam Turbine.
This boiler is a multi-pass boiler. First pass is free pass made of water-cooled membrane wall construction to ensure maximum absorption of heat and to provide structural rigidity. The water-cooled walls are distinctive membrane wall (welded wall) design and construction. This construction provides gas tight chamber, most effective utilization furnace radiant surface and significant elimination of refractory, thereby reducing the frequent refractory maintenance to a great extent. Additionally, boiler installation time is also reduced.
Optimum circulation ratio at all loads enabling efficient cooling of water wall tubes and uniform heat absorption.
Super heater and Evaporator sections are located in the second pass of the boiler and Economizer section is located in the third pass.
Fully convective super heater section ensures lower tube metal temperatures, longer life and better reliability. Super heater tubes are provided with adequate pitching to avoid ash bridging.
Plain tube, non-steaming type forced flow section with in-line arrangement ensures ease of cleaning.