Chimney heights

Holzworth, G. C., Climatic data on estimated effective chimney heights in the United States, in "Preprints of Joint Conference on Application of Air Pollution Meteorology," Nov. 29-Dec 2, 1977, Salt Lake City, UT. American Meteorological Society, Boston, 1977, pp. 80-87. 

The function of a chimney is to discharge in a manner to give adequate dispersal to the products of combustion in accordance with the third edition of the 1956 Clean Air Act Memorandum on Chimney Heights. The scope of the memorandum is as follows ... 

On medium-sized boiler plant where gas is to be the main fuel, it may have oil as a secondary standby fuel. In this case, the chimney height must be based on the grade of fuel oil capable of being burned. 

The methods of calculating proposed chimney height are clearly laid out in the Clean Air Act Memorandum, and will be based on ... 

Application for approval of the proposed chimney height should be made to the appropriate authority at an early stage of a project in order to ascertain their approval or other height they may require. Failure to do this can result in an embarrassing situation where insufficient finance has been allocated due to their requiring a larger chimney than was included in the planned costing. 

Where waste products are being incinerated, special consideration may have to be given to the resulting flue gases. This may involve having to arrive at a chimney height in conjunction with HM Inspectorate of Factories for Pollution. 

Chimney height calculations Third Edition of the 1956 Clean Air Act Memorandum 45/818... 

New furnaces have to be constructed (as far as is practicable) so as to operate smokelessly. Chimney heights are controlled (see below). Smoke Control Orders can be introduced (to control domestic smoke) and grants are available to convert fireplaces to burn authorized fuels. Smoke (other than dark smoke, which is already controlled) is dealt with by Section 16 of the 1956 Act and is, for the purposes of Part 111 of the 1936 Public Health Act, to be considered as a statutory nuisance. 

Chimney heights on new buildings are controlled by this Act. However, Section 10 was repealed by the 1968 Act (see below) as far as chimneys serving furnaces are concerned. This Section of the Act does not apply to domestic chimneys or shops or offices. 

Section 6 This Section expands on Section 10 of the 1956 Act. Under this Section, the local authorities must approve chimney heights for all furnaces with ratings as per Section 3(1). 

Chimney height caicuiations Third Edition of the 1956 Ciean Air Act Memorandum... 

The Memorandum covers furnaces with a gross heat input in the range of 0.15-150MW. (The 1968 Clean Air Act, Section 6, requires chimney height approvals for furnaces for burning fuel at a rate greater than 1.25 million BTUs per hour. This is equivalent to 0.375 MW.)... 

The first stage of the calculation is the uncorrected chimney height. This is obtained from... 

The uncorrected chimney height is then calculated by plotting the emission rate and the classification on a graph supplied in the Memorandum or by the multiplication of factors supplied ... 

The uncorrected chimney height (t/) is calculated from the sulfur dioxide emission rate Rf as previously ... 

If U is greater than Tni then U becomes the corrected chimney height. If not, calculate C from... 

This is also known as air dilution, and is a common procedure for gas-fired boilers. It is allowed for any very low-sulfur fuels (less than 0.04 per cent sulfur) or for fuels in the range 0.04-0.2 per cent S where the VLS fuels chimney heights calculation gives a lower value of U than the other fuels calculations. In these cases, the flue may terminate at the uncorrected height U so long as ... 

If the chimney were designed to avoid ground-level concentrations exceeding the nuisance level based on the Gaussian equation, we would find short-term peaks that would produce nuisance. To avoid nuisance for a 5 1 ratio of 10 minutes to peak exposure we would need to double the chimney height from that derived for the Gaussian equation. 

Both Eq (19-4) and Eq (19-5) give the concentration along the mean centerline of travel of the cloud in the x-direction, subject to the condition that Jq00 Cdz = Ct/vx- From the second of these equations it is clear that Cos is a maximum when x = H/k 1. Thus if ki is taken as 0.05, Cot is maximum at about 20 chimney heights downstream. For large values of x... 

Cross-flow trays work to the same principle as bubble cap trays they have length-wise vapor chimneys which are fixed by the U-shaped channels and hood covers. The channel breadth, chimney breadth, chimney height and hood submergence depend upon the operating conditions. 

A safe emission value would be 10 times this value, employing a good safety margin i.e. 0.25 X 10 = 250 ppm. The provisos for this would be that the emissions from the chimney must have a minimum efflux velocity for dry gases of 15 m s and for wet gases 8 m s with a chimney height that is about 2 A times the height of the factory. 

Pressure drop allowed in the system will be decided by the purchaser. This will depend on the process units connected, overall gas duct layout, ID fan capacity, chimney height, etc. 

Chimney heights and dispersion of poUution from a point source... 

The effective chimney height,/f, is made up of two components. It is the sum of the actual chimney height and the plume rise, the latter being the additional height to which the plume centre-line ascends due to its buoyancy and efflux velocity. Examination of curves in which the maximum ground-level concentration is plotted as a function of H and atmospheric stability show that x is... 

The approach to air pollution control in the US is very different to that in the UK. Rather than controlling lead via an effluent quality standard as in Britain, an ambient air quality standard is applied. The standard, set recently [11] applies to both industrial and vehicular sources of lead and is described in more detail in Section 5.5. Under this standard it is necessary for industrial sources to control emissions, and if necessary raise chimney heights to limit concentrations of lead in ambient air within the vicinity. 

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