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The concept of Zero Effluent Discharge Gasification is presented herein. The system basically comprises of an updraft coal gasifier, indirect cooling cleaning system, tar cracker cum effluent evaporator and SCADA (Supervisory Control and Data Acquisition) System. The tar and effluent water generated during the process are refired back in oxidation zone of gasifier and thus present system offers zero-discharge of any tar, VOC and effluent and thereby protects our environment. The complete description of such coal gasification system is critically discussed in terms of functioning of the instruments/components associated with this system. In general, this presented system does not discharge any effluent to the atmosphere and satisfies environmental requirements and thus emerges as a green energy technology.

Introduction

The process of gasification is defined as the thermo-chemical conversion of solid fuel feedstock into gaseous fuel. The equipment used for this conversion process is known as Gasifier. There exists a variety of gasifier namely fixed bed gasifier, entrained bed gasifier, fluidized bed gasifier, updraft gasifier, downdraft gasifier, cross draft gasifier, circulating bed gasifier, spouted bed gasifier, plasma bed gasifier, etc. Out of all these gasifiers updraft gasifiers are the most widely used gasifiers due to their simplicity and nearly trouble free operation.

In this gasifier, solid feedstock is fed from the top and the air is blown from the bottom in upward direction and the producer gas is taken out from the top. During the process of gasification, the solid feedstock passes through drying, pyrolysis, oxidation and reduction reactions in subsequent zones. The product gas produced in such updraft Gasifier typically has 20 to 25% CO, 18 to 22% H2, 0-2% CH4, 6 to 10% CO2, 6 to 12% H2O and 35 to 45% N2 and 3 to 8% tar depending on volatile content of fuel and temperature levels in Gasifier. The heating value of this producer gas lies in the range of 5 to 6 MJ/Nm3.

The major issue therefore in updraft Gasifier is the removal of moisture and tar which comes out in the form of dirty effluent and oily volatile compounds in liquid form. The earlier technologies used to have series of wet scrubbers and carbon filters to obtain clean gas. This cooling cleaning system produces liquid tar and highly contaminated effluent water which causes serious environmental hazards. Further, gas leakages in the atmosphere add to the risk of fire and hence causes health and safety problem.

In order to abate these problems, a zero effluent discharge gasification technology is proposed herein along with its comprehensive description.

1.Water Jacketed Gasifier Shell

The present gasifier is water jacketed and it acts as a heat sink which avoids heat losses to the atmosphere and produces steam which is utilized in the gasification process and thus helps in improving the efficiency of the gasifier.

Double Lock Coal Feeding System

This is a unique feature incorporated in order to avoid fugitive particulate emissions and gas leakage into the atmosphere.

Gas Cooler cum Ash Settler

The present system incorporates primary and final gas cooler cum ash settler each with lids and bottom with water seal, in order to avoid any kind of gas leakages.

Two Way Water Seal Controlled Valve

This is another salient feature of present design. The present system incorporates two sets of condensers for indirect cooling and cleaning of the producer gas. In order to divert the producer gas in any one set, instead of mechanical valve which is prone to gas leakage, a water seal controlled valve is designed.

Condensor

The major problem of old gasification technology was the cooling and cleaning of the producer gas by scrubbers and series of filters. This used to generate enormous amount of tar and contaminated effluent./

The present system incorporates indirect cooling cleaning system through two set of condensers in parallel.

Tar Catcher

The tar catcher is a wet electrostatic precipitator. The old gasification technology uses venturi scrubber to eliminate tar from producer gas. In present system tar catcher is provided. The entry and exit of this tar catcher is again water seal controlled so as to avoid any gas/ VOC leakage or air ingress to avoid possibilities of fire or explosion.

Rotary Tar Kiln cum Effluent Evaporator

In the present technology, first there is no physical movement or supply of tar and second no subsequent combustion in spray drier or any other boiler or furnace. Here a novel tar cracker is designed where in tar is cracked and reformed in presence of steam by indirect heating in a rotary tar kiln.

SCADA System

The present system utilizes most advance supervisory control and data acquisition system with static IP for online measuring, recording and transmission of data at any remote location at any GPCB/CPCB regional and central head quarters.

Emergency management plan

Under circumstances of emergency, an emergency management plan as per prevailing safety standard is provided to the user.



Environment Friendly- Powerman Gasifier Unit

Considering the trend and analyzing requirements in the market we provide you with the gasifier unit of following specifications.

Model Capacity (kcal/hr) Replacement capacity w.r.t. CNG (m3/day)
Powerman 6000 20 Lac 6000
Powerman 8000 27 Lac 8000
Powerman 10000 35 Lac 10000
Powerman 12000 41 Lac 12000
Powerman 15000 51 Lac 15000
Powerman 20000 68 Lac 20000
Powerman 25000 85 Lac 25000

Our gasifier units have come into existence only after intensive R&D for the welfare of the environment as well as the industry implementing it.