The Use of Density Meters and Microprocessors for Energy Measurement and Control

Abstract

ANSI/API 2530 shows how natural gas volume and weight flow rates may be calculated from the differential pressure across an in-line orifice plate. AGA Report No.5 uses these equations and known relationships between specific gravity and calorific value, to calculate the energy flow rate. Both publications point to weight flow rate as the simplest and most direct approach to energy flow rate and indicate much wider use for equations originally developed for natural gas. This paper discusses the advantages of density measurement and shows how a single, in-line density meter may be used with an easily programmed micro-processor to provide rapid, reliable, low-cost, on-line solutions to the flow and energy equations, without using specific gravity meters and calorimeters.

Similar techniques enable computation of calorific values to produce a so-called "flameless calorimeter" and measurement and feed-forward control of fuel gas supplies for steam generators, process furnaces, etc., thereby improving combustion and process efficiencies and promoting energy savings. These techniques increase in value as fuel costs rise and as industry is forced to use more variable gas supplies.