NOx emissions from fluidized-bed boilers

Letters to the Editor Table 7

Carbonization results for the addition of discarded tyres to coke-oven blends Carbonization results

Coking conditions

Coke-oven blends Tyre additive form

Coking time (h)

Bulk density (Ib/ft3)

1

65 mm (XI in) pieces

2.5

51.2

2

Pulverized

2.5

3

Char

2.5

Test Series

Coke quality parameters

Without additive

1.7

‘Modified’ stability (% on 3/4in) ‘Modified’ hardness (% on % in) Mean coke size (in) Breeze (% minus % in) Coke yield (%)

54-o 64.3 7.67 3.8 75.7

44.5 56.2 1.56 4.7 -

50.5

2.8

‘Modified’ stability ‘Modified’ hardness Mean coke size (in) Breeze (% minus % in) Coke yield (%)

45.0 51.8 1.81 5.6 81.0

45-2 55.4 1.77 5.7 79.2

52.3

I.3

‘Modif ied’ stability ‘Modified’ hardness Mean coke size (in) Breeze (% minus % in) Coke yield (%)

50.0 61.3 1.61 4.2 72.5

___-

Moisture (%I

___-_____

M. J. Malette, C. G. Morris, A. B. Fung and D. Grant who did the experimental work.

REFERENCES

NOx emissions from fluidized-bed

J. R. Rubber

53.6 63.4 1.82 4.1 73,9

Age 1973,

5 6

Tinker, J. New Scientist 1972, 18, 389 Beckman, J. A., Crane, G., Kay, E. L. and Laman,

48.2 61.4 1.61 3.3 72.2

105, (4),43 D. E., Beckman, J. A., Walters, J. G. and Bennett, D. J. Rep. Invest. U.S. Bur. Mines No.RI 7302, 1969 Altenau, A. G., Laman, J. R., Bennett, D. J. and Beckman, J. A. Polymer News 1971, 1 (223), 3 Grainger, L. Coke Oven Managers Year Book, 1972, p 126 Fisher, A. D. Proc. Canadian ConjI on Coal, 1971, p 45 (published by the Energy Development Sector, Canadian Department of Energy, Mines and Resources, Ottawa, Canada)

3 Wolfson, 4

1 2

With additive ____--.

boilers

Shelton Ehrlich and Robert A. Chronowski Pope, Evans and Robbins (Received 10 June 19741

Combustion

Laboratory,

Alexandria,

An article in the April 1974 issue of Fuel’ refers to work reported by Pope, Evans and Robbins in November 1968 on NO, emissions from a coal-fired, fluidized-bed combustor. Emissions of 300 to 400 ppm (referenced to 3% excess oxygen) were reported2 at that time. Reference 1 suggests that these values are ‘as high as those from conventional coal-fired furnaces’, and that ‘the high emissions are probably due to the intimate contact between the particles and the entraining air stream’. Field test data reported in June 1973j indicate that NO, emissions from conventional coal-fired boilers generally exceed 400 ppm under normal operating conditions. With operating conditions altered to achieve low NO, and at reduced load, reported values ranged from 103 g/GJ (0.24 lb/lo6 Btu fired) to 287 g/GJ (O-67 lb/lo6 Btu). Eight boilers of various designs were tested.

284

FUEL,

1974, Vol 53, October

Virginia,

USA

Intimate contact between coal particles and air within a fluidized bed may account for fixation of atmospheric nitrogen at near-equilibrium values. However, the conversion of fuel nitrogen to nitric oxide has been shown to be the predominant source of NO, emissions from an atmospheric, coal-fired fluidized-bed boiler. Results of over 8000 h of testing in a fluidized-bed boiler module, designated FBM, of 2260 kg/h (5000 lb/h) steam-generating capacity have demonstrated that NO, emissions are lower than those from conventional coal-fired furnaces. Values as low as 73 g/GJ (O-17 lb N0,/106 Btu) reported as nitrogen dioxide have been measured by an independent testing agency for the FBM at a combustion temperature of about 810°C (lSOO”F), using 3% excess oxygen and burning a coal containing l-4% nitrogen by weight on a moisture- and ash-free basis,

Letters to the Editor

Based on tests performed in the FBM at combustion temperatures of 1450-1800°F with coals containing different amounts of nitrogen (l-O-2-2%), the following empirical equation was developed to predict the NO, emission from the FBM as a function of fuel nitrogen content for operating temperatures of 785°C (1450“F) to 980°C (1800°F): NO,(vol

ppm) = 0,28 X 106(1 + 1.7N)K

(1)

K = equilibrium constant for the reaction N2 + 2N0 taken directly from the JANAF tables and N = nitrogen content of fuel (wt %) on moisture- and ashfree basis. Fuel-nitrogen conversion to NO, has been seen to be *lo%, which when added to the low thermal NO, component results in a total NO, emission substantially below the limit of 0.7 lb N02/106 Btu (~525 ppm at 3% oxygen) or 300 g/GJ set by the EPA for new large coal-fired boilers. A typical range of NO, values, in ppm, would be 200 ppm for a l-4 wt % nitrogen coal to 400 ppm for a 2.0 wt % nitrogen coal. At bed temperatures below about 1015°C (1900”F), NO, emissions generally exceed the equilibrium values where 02

+

based on the measured excess oxygen content at the furnace At temperatures above this the NO, emission is exit. substantially below equilibrium. For a typical 1.4 wt % nitrogen coal, NO, emissions followed the relation4: NO,(vol

ppm) = -350

+ 0.41 Tb

(2)

where Tb = fluidized bed temperature, OF, and 1400 < Tb < 2200”F, i.e. Nod: = -337 + 0-74Tb where Tb is in “C and 76O
Fuel,

Obituary Professor Dr-lng. W. Rademacher On 4th December 1973 the G.D.R. correspondent of Fuel, Professor Dr-Ing. Werner Rademacher, died at the age of 64. Professor Dr Rademacher was in charge of the field of Reaction and Fuel Technology in the Department of Process Technology and Silicate Processing at the Bergakademie Freiberg in Saxony. In his lectures he covered pyrolysis and the techniques of degasification, fuel engineering, power economy and layout of fuel-engineering plants. He acquired his wide experience over many years in enterprises for brown-coal processing and, since 1954, as technical director of the branch of coal processing in the Project and Design Office ‘Coal’ of the G.D.R. He deserves mention especially for the building-up of the combined gasworks ‘Schwarze Pumpe’, the biggest brown-coal processing works in the world. The results of Professor Dr Rademacher’s scientific work have found expression in about 40 publications concerning his special field. As successor in the professorship of Professor Dr Rammler, Professor Dr Rademacher exerted himself for the further development of a scientific school in the field of fuel technology. His scientific achievements were appreciated in many ways, both by high State awards of honour and membership of national and international technical committees. His scientific knowledge, practical experience and masterful guidance of men enabled Professor Dr Rademacher to direct the education of his students to the application of scientific methods of work in their later jobs in industry. In him we have lost an indefatigable researcher and a gifted teacher, whom we shall always keep in kind remembrance.

FORTHCOMING

PAPERS

The following papers have been accepted lication in future issues of FUEL:

(24 August

1974)

for pub-

Alkaneo and fatty acids in humic substances M. Schnitzer and .I. A. Neyroud Effect of inhibitors LPGlair mixtures S. K. Chakraborty,

on flammability

range of flames producedfrom

B. N. Mukhopadhyay

and B. C. Chanda

Prospects for nuclear fusion reactors S. E. Hunt

Klose, Toufar, Born

FUEL, 1974, Vol 53, October

285