Agriculture Reference
In-Depth Information
At higher fluidizing velocities CO does not have sufficient time to convert to CO
2
and
thus CO emissions increase. Thus increase in excess air can work both ways. On one hand
excess air can reduce CO emissions by providing more oxygen to convert CO to CO
2
and on
the other hand it can increase CO emissions by increasing fluidizing velocity which can force
the produced CO to leave the combustor unburned. Thus, the results can be explained on the
basis that at lower excess air levels CO emissions are higher due to lack of oxygen
availability. When excess air is increased, CO emissions decrease because of oxygen
availability which converts CO to CO
2
. At even higher excess air levels, CO emissions
increase due to higher fluidizing velocity and lower bed temperature.
The volatiles evolve and leave the bed unburned possibly due to lower residence time.
During coal-pulp blends combustion CO emissions are found to be first increasing with
increase in blending ratio (increase in the pulp proportion in the blend) and then decreasing.
The emissions increase from 1000 - 2500 ppm for 70/30 blend to 1200 - 2900 for 60/40
blend possibly due to increased moisture which hinders access of oxygen to coal particles.
With further increase in pulp proportion the emissions decrease to 600 - 1400 ppm which
may be due to delayed ignition at higher moisture content.
5.
F
LUIDIZED
B
ED
B
EHAVIOUR
A
SSESSMENT
OF THE
B
Y
-P
RODUCTS
Vinasse and raffinate were co-fired with coal. The raffinate was also co-fired with natural
gas to assess the influence of coal ash on bed behaviour. Moreover, prolonged tests with pulp
were undertaken using optimum blend (50/50; coal/pulp) to study the feasibility of this
material for this particular application for energy recovery. Experimental details of the tests
can help in designing suitable energy recovery systems of the future in the sugar industry
using beet sugar as a raw material.
5.1. Co-Firing of Raffinate with Coal
Raffinate was cofired with Thoresby singles coal. Raffinate has a viscosity of 150 mpa.s
(0.15 kg/m.s) and density of 1320 kg/m
3
. The coal used for the tests was 6 - 10 mm size.
The conditions of the test are given in Table 17. The resultant bed and freeboard
temperatures as well as the pressure drop across the bed during this test are presented against
time in Figure 9.
Approximately 40 minutes after the start of co-firing the pressure drop experienced a
sharp fall which was associated with the onset of agglomeration and partial de-fluidization of
the bed. Under these latter conditions, the pressure drop is no longer associated with
supporting the mass of the suspended bed particles and hence falls to a value of that for a
partially “packed” bed. The phenomena of bed agglomeration results in temperature gradients
in the bed and according to Armesto et al. (2002) large fluctuations in the bed pressure are
first signs of onset of agglomeration. In Drift and Olsen, (1999) view point, upon onset of
agglomeration, temperatures within the bed start to deviate.
