Calorific value meters

The volume of gaseous fuels used can be measured accurately with turbine meters. However, to measure their mass, it is essential to apply temperature and pressure corrections to the measured volume. Changes have been observed of over 2 % in the calorific value of natural gas — sufficient to cause a significant change in the degree of burning. As a result, many operators have installed calorific value meters to detect any changes as they occur. 

Customers without calorific value metering can regulate their offtakes only by means of a pre-set average calorific value. In view of the necessary safety margins it is not possible to make economically optimum use of the contractually provided volumes, even when an arithmetic average of the upper calorific values is used for invoicing purposes. 

An accmate heat volume regulation is only possible if the periods for heat volume formation are shorter. This calls for investments, however, in calorific value metering, small computers and the relevant software. Such regulating procednres, e.g. also by process computer, are only economically jnstified in the case of large throughputs. 

The flow diagram for a rich gas plant producing gas with a calorific value of 710 Biu/slandard cubic foot is shown in Fig. 1. The product is used to enrich lean gas from an IC1 (Imperial Chemical Industries) naphtha reformer which has a calorific value of about 320 Btu/standard cubic foot to the town gas standard of 500 Btu/standard cubic foot (56 Calories/cubic meter). Typical gas analyses arc given in Table 1. 

Gross calorific value This is the heat value of energy per unit volume at standard conditions, expressed in terms of kilocalorie per cubic Newton meter (kcal/Nm3) or other equivalent units. 

The High Calorific Value of the oil shales was determined by a "bomb" calorimeter on more than 90 composite samples from different deposits and on one-meter samples along borehole sections. The average value is lOOOKcal/Kg and the highest value measured was 1790Kcal/Kg. The correlation between organic matter content and the calorific value is more than significant (R=0.96). The equation for the Ef e deposit is ... 

The pulverized coal fed to the burner should be very steady with low fluctuation of set flow rate of the metering system. The variability of raw coal in terms of calorific value is mainly due to the fluctuation in moisture... 

At Senboku Works II, we are now using sonic calorimetry to monitor calorific values in LNG at unloading, and use Rauter meters for calorific value control of feed gas our optical interferometer is now undergoing field tests and further development to exploit the method s theoretical advantages in terms of high-speed response, high sensitivity, and simplicity and compactness of the apparatus. 

Since Senboku Works II came on stream in 1977, we have used a Cutler-Hammer combustion-type calorimeter for calorific value monitoring and quality control, and a Rauter meter for gas density monitoring. 

As we mentioned, however, we now know the correlation between calorific value and density, and we have compared the performance of the two methods operating in parallel, confirming that the Rauter meter s rapid response and high reliability make it fully adequate for calorific value control. 

Figure 13 shows sample data for the Rauter meter in control measurement apphcations. It controls calorific value to within 20 kcal/Nm Because LNG is clean, there is little error caused by contamination of the apparatus and the apparatus remains accurate if given a regular yearly inspection. 

The second method of measuring energy flow using independent measurements of volumetric flow was provided by a Lone Star Gas orifice meter. Input to the Elliot flow computer included the pressure differential across the orifice plate and the pressure and temperature of the gas at the orifice. A conunercial GB-2000 instrument from Precision Measurement Incorporated provided a continuous input of specific gravity to the flow computer. Calorific value also was provided by the GB-2000. The flow computer used these inputs to calculate the volumetric flow at standard conditions. It then corrected for... 

---