Michael Möller, Product manager for vortex flowmeters at KROHNE
Energy management: Integrated measuring technology solutions to determine energy flows in the operation
Given the rising costs of raw materials and energy, companies must now come to terms with the issue of energy management more than ever before. An essential building block here is in-house energy balancing. It helps reduce energy costs while saving over the long term, providing the option of identifying the energy requirements of the various parts of the company and assigning them according to cost.In many companies, compressed air, steam, hot water and natural gas are the main sources of energy used, in addition to electric energy. The greatest potential for energy savings can be found in these auxiliary and supply circuits: steam boiler monitoring, measurement of burner consumption or the monitoring of compressed air supply networks including monitoring the free air delivery (FAD) for compressors are the typical cornerstones of the energy management that can be achieved with the help of process measurement technology. Measuring the amount of energy depends on the set-up and the accuracy of the measuring devices used. Typical applications and their challenges are introduced below.
Steam: accurately measuring quantities of energy and burner consumption
Even though steam boilers have an extremely high degree of efficiency, the efficiency of the steam system as a whole is considerably lower. Reasons for this include non-insulated steam lines, leaks, contaminants or faulty condensate separators. People often overlook the pressure and temperature fluctuations that can occur during the process. However, such fluctuations have a considerable impact on the measuring error of a measuring system (Table 1), which can result in a high loss of energy. For this reason, measuring devices used to measure quantities of steam energy must be fitted with pressure and temperature compensation (online density compensation). Typical measuring systems are thus located behind a boiler or in front of large outlets (plant or building entrance dimensions). The measurements can help identify losses and increase the efficiency of the steam system.
In direct correlation to the measurement of steam quantity is the measurement of burner consumption which is used to calculate the amount of natural gas used in relation to the amount of steam produced. The result is an index for the degree of efficiency of the steam boiler and can, for example, be used to get an idea of the maintenance required in the future.
Table 1: Energy costs when measuring saturated steam or superheated steam (*nominal pipe size DN100, 50 % capacity, energy costs 60 €/MWh)
Compressed air: using and maintaining compressors more effectively
There must always be sufficient compressed air of appropriate quality at the right pressure level in a system. Energy efficiency depends partially on accurate systems for measurement and control and partly on the degree of efficiency of the compressor. Potential measuring errors are shown in Table 2. When measuring air consumption leaks are the most frequently occurring difficulty. They lead to increased running times for the compressor as well as increased energy consumption and more frequent maintenance. A well-maintained compressor running at maximum efficiency has a degree of efficiency of 85%. For this reason it is necessary to know the free air delivery (FAD) of a compressor as it also gives the user information about maintenance requirements and energy efficiency.
The free air delivery, FAD, is the amount of free air that can be taken in through the compressor at the inlet on the suction side. Measuring the free air delivery helps with the optimal scheduling of maintenance intervals and when it comes to operating the compressor at the highest possible degree of efficiency. Monitoring the degree of efficiency is particularly of interest given the comparatively high energy consumption of the compressor.
Table 2: Non-measured energy costs through measuring errors during pressure and temperature fluctuations in the compressed air supply network (**nominal pipe size DN100, 50 % capacity, energy costs 75 €/1000 Nm³)
Figure1 : Monitoring a compressed air supply network using vortex flowmeters with integrated pressure and temperature compensation
Heat and cold energy: monitoring down to the machine level
When measuring warm energy, a flowmeter along with two temperature sensors and a calculator are used to bill warm energy. Depending on the operation, the generated quantity of hot water is made available to the different parts of the operation via a wide-reaching network, where monitoring takes place right down to the individual machines. The same is true for cold energy measurement: one typical application for cold energy measurement would be a large refrigerating machine that serves a business or a building. Air conditioning units use the supplied cold to cool the surrounding air and return warm water. The cold energy consumed can be calculated using the flow volume measured and the difference in temperature between the supply and return.
Save costs on installation and achieve increased accuracy by using compact measuring systems
At first glance, measuring devices used to measure quantities of energy are no different than the “normal” process measuring devices. Vortex flowmeters are frequently used to measure steam, compressed air, hot water/condensate and natural gas. In order to measure fluctuations in pressure and temperature, “classical” measuring systems consisting of a vortex flowmeter, a separate pressure sensor and a separate temperature sensor as well as an additional flow calculator are used. This results in high costs for assembly and installation.
However, with the installation of a vortex flowmeter featuring integrated pressure and temperature compensation as well as an integrated energy quantity calculator such as the OPTISWIRL 4200 C, there is no need to install separate sensors, cables and infeeds. Thanks to the combination of three measurements (flow rate, temperature and pressure) in one 2-wire device, the line must only be opened at one spot. This results in total savings of up to 50% of the costs per measuring system.
About 90% of all vortex flowmeters are designed one size smaller than the line diameter in order to increase the flow speed and to get a wider measuring range. OPTISWIRL is thus available in a version with integrated reduction of nominal diameter for space-saving installations and large measuring spans. This eliminates the need for reducers and expanders in the line before and after the device. Like all OPTISWIRL devices, these versions are wet calibrated using special vortex calibration rigs prior to delivery.
A further advantage of compact measuring systems is their higher measuring accuracy: with the classic installation, all errors in the measuring chain must be taken into account to determine the accuracy of the system. This can result in a measuring error between 3…5 %. With a compact measuring device, all three integrated measurements are calibrated together, achieving a system accuracy of 1.5 % of the measured value.
Figure 2: Different system accuracies for classical and integrated systems
In addition to gross heat calculation for steam, the OPTISWIRL 4200 now includes net heat calculation for steam and condensate/hot water. With one temperature sensor integrated as standard, the device can be installed as an (in-house) heat meter in the feed line directly connected to an external temperature assembly in the return line. The gross and net heat values can be fed directly into a DCS to support in-house energy management.
Conclusion
An energy management system allows companies to benefit from tax advantages. In addition to electrical energy, compressed air, steam, hot water/condensate and natural gas are all typical energy sources in producing companies. Measuring these currents using measurement technology solutions that feature integrated sensors and special functions for energy measurement has numerous advantages. Using a vortex flowmeter with integrated pressure and temperature compensation makes it possible to not only lower installation costs but also to increase the measuring accuracy of the system. In addition, costs for additional sensors and devices and their wiring are also eliminated.
Contact: KROHNE South Africa
John Alexander email: [email protected] Tel.: 011 314 1391