This document discusses the calculation of steam drum level in a boiler. It provides equations to calculate the saturated water level (h) in the drum and the differential pressure across the drum (ΔP) based on the total height of the drum (H), density of saturated water (dw), and density of saturated steam (ds). It also describes how to calculate the actual compensated drum level percentage that accounts for changes in water and steam densities with drum pressure. An example is provided to illustrate how drum level readings from the field transmitter map to values in the distributed control system and calculation block.

1. Date : 05.06.2018
Document no : Rev: 01
Page 1 of 4 Boiler Commissioning – Project Management
STEAM DRUM LEVEL CALCULATION
Prepared By: Ashish S. Kinkar
GET (Boiler Commissioning – Project Management, tKII Pune)
Submitted to: Mahimmay Paul
Sr. Executive (Boiler Commissioning – Project Management, tKII Pune)
Date: 13.04.2018
Thyssenkrupp Industries India Pvt. Ltd.
Pimpri, Pune

2. Date : 05.06.2018
Document no : Rev: 01
DRUM LEVEL CALCULATION
Where,
H –Total height of the drum (mmWc)
h - Saturated water level in drum (mmWc)
dw – Density of saturated water (g/cc)
ds – Density of saturated steam (g/cc)
∆P – Differential pressure across drum (mmWc)
CP – condensing pot
∆P = {[(h.dw + (H-h) ds +P] – [(H + P)]}
∆P = h (dw-ds) + H.ds – H
Page 2 of 4 Boiler Commissioning
Saturated water level in drum (mmWc)
Differential pressure across drum (mmWc)
Commissioning – Project Management

3. Date : 05.06.2018
Document no : Rev: 01
Page 3 of 4 Boiler Commissioning – Project Management
= {(
∆
) − ( )}
∆
x 100 = LT %,
This is the actual compensated drum level
Fig. density of saturated water and steam according to drum pressure
𝒉
𝑯
∗ 𝟏𝟎𝟎 =
𝐋𝐓%
𝒅𝒘 𝒅𝒔
−
𝒅𝒔
𝒅𝒘 𝒅𝒔
∗100
𝒉
𝑯
x100 = Actual drum level

4. Date : 05.06.2018
Document no : Rev: 01
Page 4 of 4 Boiler Commissioning – Project Management
EXAMPLE:
Let us assume,
H = 800 mm
1. For field Level transmitter:
LRV = -800 mm, URV = 0 mmWc
2. In DCS Scale value
LRV = -400 mmWc, URV = +400 mmWc
3. In calculation block, scale value
LRV = 0 mmWc, URV =800 mmWc
Hence when drum level (field transmitter reading) = -400 mmWc
DCS value =0 mmWc, and
Calculator block = 400 mmWc
Hence
𝟒𝟎𝟎
𝟖𝟎𝟎
𝐱 𝟏𝟎𝟎 = 𝟓𝟎% … … … … … … … … … … … 𝒉
𝑯
x100
NOTE:
In actual case, due to drum pressure the value of saturated water and steam density will decrease and
hence the drum level. After considering the density compensation, we will get actual level.