| Abstract |
Challenges of measuring geothermal steam flow include: long transmission lines from the well to the plant; temperature and pressure variation; as well as the changing composition of the steam from non-condensable gases. With the long transmission lines, significant pressure drop is experienced and cannot be recovered. Permanent pressure loss (PPL), can be significantly reduced with the use of proper flowmeter technologies. Flow transmitters that measure the changing pressures and temperatures will help maintain expected flow rate accuracy. Pressure and temperature of the steam coming out of the well are variable in nature. The calculations of mass flow or energy often do not take these variations into account accurately or in real time. Usually an average density value is used in the flow calculation rather than compensating for these variations in real time. Other variables in the flow equation are set and not compensated for dynamically. These practices can cause dramatic increases in inaccuracies and can often lead to further errors when these values are compounded in the flow equation calculations. Multi-Variable transmitters can do the work of the compensation in the field and therefore allow for other important I/O space to be saved for other parts of the process. This limits expensive and scan time requirements within the DCS or Host computer. The “real-time” compensation with the Multi-Variable of both temperature and pressure as well as compensation of other potential bias errors assures for the best possible use of computer space, scan time while assuring accurate flow measurement information. Given that many measurement points are used for “royalty calculations”, timely and accurate measurement data is a must to proper accounting of a well’s production. Geothermal steam, by its very nature, contains many minerals and elements that can plate out and plug holes and crevices in existing flowmeters. Meters Without cracks and crevices, such as some vortex meters can compensate dynamically for process temperature changes are one possible solution. The accuracy of vortex flow meters is not dependent, in part, on the edge of the shedder bar remaining sharp as is required for orifice plate installations. Vortex meters are generally considered to be low pressure drop devices also. The result of our research/experience into ways to expand the range of primary flow elements and decrease the cost and performance of these devices over their installed life cycle, indicates that improvements can be achieved through the use of top-mounted d/p flow devices and vortex meters particularly in steam applications. Finally, our experience shows that differential pressure devices direct-mounted on the primary flowmeter reduce the potential for measurement errors significantly as well as reducing installation and maintenance costs. Impulse lines and leak points are eliminated or reduced when direct mounted transmitters are used with primary flow elements. |