Question

Determine the height of the chimney to produce a static draught of 22mm of water if the mean flue gas temperature in chimney is 290^oC and ambient temperature in boiler house is 20^oC. The gas constant for air is 29.26Kgm/Kgk and for chimney flue gas is 26.2 Kgfm/Kgk. Assume reading as 760mm of mercury?

(a) 38.42m

(b) 42.55m

(c) 45.84m

(d) 44.03m

This question was posed to me during a job interview.

I need to ask this question from Draught System topic in chapter Steam Generators & Accessories of Energy Engineering

Answer 1

Correct answer is (b) 42.55m

For explanation I would say: Density of air at 290K ρg = P/RT = [1.033 * 10^4 / 29.26 * 290]

                    = 1.217Kg/m^3

          Density of fuel gas at 563K, ρg = [1.033 * 10^4 / 26.2 * 563]

                     = 0.7 Kg/m^3

  Static Draught, p = H (ρa– ρg)

                       22 = H (1.217 – 0.7)

                H = 42.55m