14


Measurement and Testing


REFINERY BOILER REPLACEMENT PROJECT’S AIR & FUEL GAS MEASUREMENT CHALLENGES SOLVED WITH PRECISION MULTIPOINT THERMAL FLOW METER


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Figure 1: End-Customer Refi nery


When the process and plant engineers at a major oil sands refi nery in the province of Alberta, Canada, needed to replace their boiler system to upgrade its effi ciency and thereby reduce its fuel costs and carbon footprint, they faced several technical challenges. Among them was the optimisation of the forced air fl ow to fuel gas ratio that would optimise the boiler fl ame burn rate for the most consistent, lowest cost heating under all operational and weather conditions.


As the price of natural gas for industrial heating processes and plant electric power continues to rise due to limited supply access, clean air emissions controls are also growing more stringent too. For these reasons, there is a need for petrochemical and other industrial process companies to more tightly control heating processes involving burners, boilers, furnaces, ovens, kilns, dryers, oxidisers and fl are stacks (as well as reduce their electric power costs).


Many process and plant engineers will be familiar with some form of the old adage, “You can’t control what you don’t measure accurately.” Fortunately, there are many process heating best practices that can be incorporated into industrial process plant operations. The one thing all of these enhancements depend on, however, is accurate, consistent air/gas fl ow measurement to control the burn and assure highly effi cient heating.


The refi nery’s boiler replacement project plant team engaged a major engineering, production and construction (EPC) fi rm. To operate the boiler at optimum effi ciency and maintain safe operating conditions (Figure 1), three critical air/gas fl ow measurements were identifi ed early as critical to project success: (1) forced draft air, (2) combustion air and (3) fuel/fl ue gas recirculation.


The Problem The original specifi cations developed for the boiler project identifi ed averaging pitot tube fl ow measurement technology for the air fl ow measurements, but the EPC quickly realised that the technology was limited in its fl ow range capability and would require much


more effort to maintain for the refi nery team. For these reasons, the engineers decided to review other fl ow measurement technology options that might be a better fi t for the project.


Large boiler applications always come with challenges. Properly evaluating the measurement is relatively easy. Determining the ideal meter location gets challenging when existing plant equipment layout access and clearances are considered in addition to the measurement accuracy objectives. A lot of work went in to selecting locations that not only could be measured accurately, but also didn’t pose an issue when it came to installation and maintenance of the instruments. The following meter location requirements were identifi ed:


Forced Draft Air Inlet (Figure 2) • 120x33-inch [3,048 x 838 mm] cross section of duct


• Two ducts, each with two 4-point air fl ow meter systems for redundant measurement • Four air sensor points per meter for optimal performance


• Air fl ow rate: 1,901 to 190,100 lbm/hr fl ow range [862 to 86,277 kg/hr] • Accuracy: Less than 5% of reading


Combustion Air • 63x50-inch [1,600 x 1,270 mm] cross section of duct


• One duct with three 2-point air fl ow meters systems for redundant measurement • Two air sensor points per meter for optimal performance


• Air fl ow rate: 4,710 to 471,000 lbm/hr [2,136 to 213,642 kg/hr] • Accuracy: Less than 5% of reading


Flue Gas Recirculation Line (Figure 3) • 41.25-inch [1,048 mm] pipe (inner diameter) • One gas fl ow meter 3-point system


• Gas fl ow rate: 626.7 to 62,670 lbm/hr [284.3 to 28,427 kg/hr] • Two calibration groups: natural gas or refi nery fuel gas


• Accuracy: Less than 3% of reading Figure 3: Fuel Gas / Flue Gas Recirculation Figure 2: Forced Air (Aleksandrs Kenenkovs | Adobe Stock Images)


PIN OCTOBER / NOVEMBER 2023


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