Biomass slurry (Coconut shell powder, diesel and water) combustion system considered in this problem is a simple cylindrical furnace of size 0.35m diameter by 0.56m height. The inlet to the furnace is at the bottom and the fuel enters the furnace in a sprayed form at 70m/s. Biomass slurry enters the furnace at the bottom with an average mass flow rate of 0.2m/s depending on the composition of the fuel. The furnace has a constant temperature of 12000C. The fuel supply to the furnace is from two tanks, one is the oil tank and the other is the slurry tank, compressed air connection is provided to the slurry tank to create pumping action whenever it is required. The outlets of both the pipes of the tanks

BIOMASS SLURRY FIRED-FURNACE Fig. 1

The problem with the above setup was that the consumption of the biomass slurry fuel was much faster than that of the diesel and the efficiency of the furnace with biomass slurry as fuel was far less. So to overcome this problem a detailed flow analysis of the fuel into the furnace from the nozzle at different inlet angles was done as shown in fig.2a & 2b.

are connected to a single pipe at the nozzle. By controlling the valves, fuel supply to the burner can be had from anyone of the tanks. The burner used in the experimental setup consists of a central hole through which the liquid fuel or slurry flows. Operating the fuel valve at the base of the fuel tank controls the rate of flow of fuel from it. The atomization rate can be controlled using the needle valve. There are two airports, one for the primary air supply and the other for the secondary air supply. In the primary air supply line a continuous helical path is provided to create swirling of air. At the exit a nozzle is provided as shown in fig.1. The sudden expansion of air creates vacuum, which helps to draw the fuel from the fuel nozzle. Over the primary air passage, the secondary air passage is provided. The air enters tangentially to this passage. This has been provided in order to create further swirl. Operating the gates provided in the main entrance can control the quantity of air supply and the fuel supply.

2a. Finite Volume Modeling of the Furnace using Gambit

GAMBIT is a preprocessing software developed by Fluent inc, USA, the advantage of using GAMBIT is it has a single interface for geometry creation and meshing that brings together all of Fluent’s preprocessing technologies in one environment. Advanced tools for journaling let you edit and conveniently replay model building sessions for parametric studies.

FLUENT is the world leading CFD code for a wide range of flow modeling applications. With its long-standing reputation of being user-friendly, FLUENT makes it easy for new users to come up to productive speed. Its unique capabilities in an unstructured, finite volume based solver are near ideal in parallel performance.

Dimensions of the furnace Height of the furnace: 810mm

Outer Diameter of the furnace: 930mm Inner Diameter of the furnace: 570mm

For easy meshing the furnace was divided into three sections as shown in the following fig., because of the continuity in meshing the whole furnace though divided into three sections is considered has a single volume. For analysis purpose, the combustion chamber was modeled with different inlet conditions.

Model-I: Inlet hole inclination = 0 deg., Inlet diameter = 30mm, with top fully open. Fig3a MESHED MODEL Fig.3b

Model-II: Since in the Model-2a the inlet was exactly at 90deg., the solid

particles used to make a direct impact on the cylinder wall and come out of the furnace unburnt where in the residence time of the fuel was very small, so the inlet i. e. the nozzle position was inclined at various angles to get the optimum swirling of the fuel in the furnace as shown in the following analysis.

Inlet Inclination = 45 deg with respect to x and z axis Inlet diameter = 30 mm & 75 deg from positive y-axis, with top fully open The Cylinder was divided into 3 sections for easy meshing as shown below

MODEL-III: REFINED MODELING OF THE FURNACE WITH TOP PARTIALLY OPEN

Dimensions of the furnace I. Height of the furnace: 810mm

2.Outer Dia. of the furnace: 930mm 3.Inner Dia. of the furnace: 570mm 4.Inlet Dia. = 30mm

5.Outlet diameter = 140mm: Inclination of the inlet = 45 deg, with respect to x and z axis 75 deg from positive y — axis

For easy meshing the furnace was modeled as two separate sections as shown in the following fig., and was combined using t-merge for analysis.

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Fig4a

MESHED MODEL Fig.4b

Fig.5a Fig.5b

For analysis purpose, the combustion chamber was modeled with different inlet conditions.

Fig.5a Bottom section of the combustion chamber with the inlet diameter=30mm Fig.5b Top section of the combustion chamber with the outlet 140mm

2. Results and discussions:

MODEL-I: With top fully open and the inlet angle of 45 degrees.

Material used to visualize the flow is Biomass and air, Inlet dia = 30mm and Outlet 570mm. For initialization: Inlet conditions: 700m/s; outlet condition =

101325 Pa Path Unas Colored by Sialic Prassure фзкаї) Dec (ft. 20CM FLUENT 6 0 iSfi legrewled. lo Щ

Fig.6

Residence time of the fuel in the furnace = Total length of the path line

Velocity of the inlet fuel = nd(number of rounds)

700m/sec

= П(0.35)(1.5) = 0.002356sec’s 700

From the above velocity inlet path lines, static pressure, total pressure and velocity flow lines it has been concluded that the biomass particles used to not completely burn in the furnace after impact the solid particles used to impinge out of the furnace unburnt, since the top of the furnace was not closed, so the furnace was remodeled as shown in the following fig. With a small and the most optimum opening for the exhaust gases to escape out of the furnace.

MODEL-II: With top partially open and the inlet angle of 45 degrees.

For initialization:

Fig.7

Material — air Inlet conditions: 700m/s; outlet condition = 101325 Pa With material as Biomass volatiles with a density of 200 kg/m3 Inclination of the inlet = 45 deg w. r.t x and z axis 75 deg from positive y-axis

Residence time of the fuel in the furnace = Total length of the path line

Velocity of the inlet fuel = nd(number of rounds) 700m/sec

= П(0.35)(4) = 0.006283sec’s 700

From the above calculation of residence time of the fuel in the furnace it is clear that the residence time was increased from 0.002356sec’s to0.006283sec’s.

3. CONCLUSIONS:

From the study of the above path lines it has been concluded that the optimum circulation of the fuel has been obtained in the furnace and there is hardly any fuel escaping out of the furnace and complete combustion of the fuel is taking place inside the furnace because of the increase in the residence time of the fuel. With this result the efficiency of the furnace was increased from 25% to 65% and with these results 80W of power was generated and the same furnace was very easily used to melt Al of 4kgs/melt. Based on the above flow analysis and combustion analysis and on the same principles, analysis of combustion of Biomass slurry in I. C.engines can be done with at most ease.