Loss of steam through steam traps accounts for significant energy waste at many plants. Quantifying the extent of the loss often poses difficulties. Indeed, to date, no simple-to-use predictive tool can accurately estimate the actual rates of lost steam as a function of steam line pressure and saturation temperature of sub-cooled condensate. Here, however, we present an accurate and reliable method that requires fewer computations than conventional approaches.

The tool predicts the condensate flow, Q, in kg/h, via a simple equation:

Ln(Q) = a + b/P + c/P² + d/P³ (1)

where P is steam line pressure in kPa (abs) and the four coefficients relate to the sub-cooled condensate's saturation temperature, T, in K, via:

a = A₁ + B₁T + C₁T² + D₁T³(2)
b = A₂ + B₂T + C₂T² + D₂T³ (3)
c = A₃ + B₃T + C₃T² + D₃T³ (4)
d = A₄ + B₄T + C₄T² + D₄^T3 (5)

The optimum tuned coefficients (A, B, C and D) appear in Table 1. They cover condensate flow rates for steam traps with a flow capability, C_V, of 1 in data reported in the 4th edition of C. R. Branan's "Rules of Thumb for Chemical Engineers," Gulf Publishing (2005).

In the next step, the result from Eq. 1 is used to estimate actual loss of steam. Equation 6 gives the corrected steam-trap flow factor:

F_C = Q_C/Q (6)

Equation 7 then predicts actual steam loss, SA, as a function of trap inlet pressure, in kPa (abs), and the corrected flow factor:

S_A = (0.093P – 9.4589) F_C (7)

Figure 1 compares the tool's predictions of condensate flow rates in steam traps with C_V = 1 as a function of steam line pressure and saturation temperature of sub-cooled condensate with data reported by Branan. The results agree well with these data. Figure 2 depicts the tool's performance for estimating condensate flow rates as a function of steam line pressure and saturation temperature of sub-cooled condensate. Figure 3 compares predicted steam loss as a function of inlet pressure with Branan's data. Table 2 highlights the very good agreement with the reported data — the average absolute deviation is 2.87%.

AN EXAMPLE