Steam Quality And Metering
Authors: Wilson M. 
Published: March 2010

Field tests were conducted to determine the absolute pressure-differential pressure-quality-mass throughput relationships for wet high-pressure steam in orifice and flow-nozzle meter runs. Adequate relationships were established and, with the aid of an empirical correlationfor sharp-edged orifices provided by a New Zealand researcher, a means is presented to determine steam quality in a flowline when the mass throughput rate is determined by a1t independent method.

As an aid in calculating steam quality at the output of once-through steam generators, two monographs were developed and are presented.

Introduction

The work and results presented in this paper have evolved from Imperial Oil Limited's thermal recovery pilots at Cold Lake, Alberta. At these pilots, wet steam is being used as the heating medium to improve the mobility of a very viscous reservoir crude. It is important to know the quality of the steam being produced, and further to be able to determine mass and heat input to each injection well.

In 1968 and 1969. a series of field tests were conducted to determine the performance of conventional metering devices in two-phase service.

Figure 1 illustrates the type of steam generating and metering equipment involved. Input water to the generators is measured with turbine meters and output steam is metered with orifice plates; individual well lines are monitored with flow nozzles. The generators are of the once-through type and are typically used to produce 80 per cent quality steam. This type of steam generator has the advantage in that only minimum, water treatment is required. The remaining liquid phase is capable of carrying water-soluble solids in solution. If dry or superheated steam was produced, it would be necessary to deionize the feed-water at considerably greater capital and operating cost, or dispose of a water phase containing all dissolved solids. A disadvantage exists, however, because the metering of two-phase streams is not nearly as advanced as the state-of-the-art for single-phase streams. This has fiven rise to the problems considered in this paper.

Two general problem areas are involved. First, how can the output steam quality from each generator be adequately determined by a simple procedure ? Second, how do conventional metering devices - orifice and flow-nozzle uns, specifically - perform with twophase streams? To some extent. the two problems are interrelated, because the answer to the second helped solve the first.

Generator output quality is required for three reasons. First, it is desirable to know the total energy input to the injection system so it can be compared with the total energy injected at wells. If a reasonable energy balance cannot be obtained, this is an indication that one or more of the metering devices is not functioning properly and maintenance is required. Second, output quality from each generator is required by plant 8perators to insure that generator firing rates are properly set and stay in adjustment. Third, it is desirable to compare energy output from a generator with fuel consumption on a regular basis to detect changes in generator efficiency.