tailieunhanh - A Heat Transfer Textbook Third Edition by John H Lienhard IV and John H Lienhard V_4

Tham khảo tài liệu 'a heat transfer textbook third edition by john h lienhard iv and john h lienhard v_4', kỹ thuật - công nghệ, điện - điện tử phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | TM 5-650 APPENDIX D BOILER WATER CALCULATIONS D-l. BOILER BLOWDOWN CALCULATIONS The rate of blowdown from a boiler is a critical operating control on total dissolved solids paragraph 4-4c . a. The water added to the boiler must equal water lost from the boiler F E B Where F Feedwater pounds hour E Steam generation pounds hour B Blowdown pounds hour b. The blowdown can be related to the feedwater using the cycles of concentration C _EorF BxC B Where c Cycles of concentration no units F Feed water pound hour B Blowdown pound hour It is common to express blowdown as a present. B 100 c c. The relationship between feedwater blowdown steam generation and cycles is represented as B E C-l This is derived as follows 1 F B X c paragraph C-lb 2 F E B paragraph C-la 3 B X c - E B Replacing F in Equation 2 with 4 B X c - B E 5 Bx C-l E 6 B E C-l b. Blowdown Equation 1 Rearranging Equation 3 Rearranging Equation 4 Rearranging Equation 5 never metered but it can be calculated if any two of the feed water cycles or steam generation quantities are known. Steam is usually metered. The cycles of concentration can be determined by comparing the concentration of dissolved solids in the boiler water to the concentration in the feedwater. Cycles can than be calculated note that the blowdown concentration is the same as the boiler concentration c _Bs or c _B mmho Fs F mmho Where c Cycles of concentration no unit Bs Blowdown TDS ppm Fs Feedwater TDS ppm B mmho Blowdown conductivity micromho F mmho Feed water conductivity micromho D-2. DETERMINING FEEDWATER REQUIREMENTS The blowdown calculations in paragraph D-l can be used to determine feedwater requirements. Note that feedwater means the water that is fed to the boiler from the deaerator and includes makeup plus condensate return. a. Example D-l. A 250 psig boiler operates at a conductivity level of 5500 mmho see paragraph 4-5a for guidance on the maximum allowable level . The boiler feedwater has a conductivity of 275 mmho. The cycles of