The Industrial Park Kleefse Waard (IPKW) in Arnhem, the Netherlands, was once an important production site for cellulose and nitrocellulose. Today, the industrial complex is home to manufacturing companies from various sectors and has become a pioneer in the sustainable production and use of energy. The operating company has set itself the goal of making the IPKW the most environmentally friendly industrial site in the Netherlands. To this end, the operator is investing in the expansion of renewable energy generation at the site.
Stork Thermeq, a leading global solution provider for steam generation and heat recovery in industrial plants, was commissioned to build a new biomass cogeneration plant. The cogeneration plant will supply sustainably produced heat and electricity to the companies on the industrial park and will also supply households in the city of Arnhem via the district heating network.
Cogeneration – the combined production of heat and power (CHP) – is considered particularly sustainable. The plant is therefore in principle eligible for aid under the national Combined Heat and Power Act (CHP Act). The heat and electricity generated by cogeneration is also subsidised by feed-in tariffs.
Stork Thermeq turned the existing boiler plant into a state-of-the-art biomass-fired CHP plant. Due to the high demand for steam for the district heating network, the CHP has been equipped with a back-pressure turbine. The high-pressure steam flow produced by the biomass steam boiler is split into two streams. One stream of high-pressure steam is directly supplied to the industrial enterprises on the industrial park and the other is used for electricity production via a back-pressure turbine. The remaining heat in the low-pressure steam from the turbine is then further utilised in the district heating network.
In terms of measurement, the plant must be designed so that the operator can bill the process steam consumed by the industrial estate’s customers. In addition, the sustainably produced energy (electricity and steam) is subject to verification as soon as the state subsidies and feed-in tariffs are claimed. The rule applies here that only heat and electricity from CHP plants can be invoiced. Biomass CHPs must therefore also be strictly separated metrologically from other plant components (e.g. auxiliary boilers and other heat sources) that are not part of sustainable energy production.
The measurement of the energy flows is carried out in accordance with the Measuring Instruments Directive (MID) and the applicable calibration law. This applies, for example, to the billing of hot water (MI-004/ OIML R-117). However, not all media are defined in the MID. No valid calibration law applies for the billing of heat energy (steam). For the metrological design of measuring points, the best available technology is to be considered here. Appropriate measuring procedures are to be used to ensure the highest possible accuracy. This for example requires measuring instruments to be traceably calibrated.
Stork Thermeq required instrumentation for process control and for billing and verification purposes for several measuring points. Particular attention was paid to steam measurements. The measurement technology had to be accurate in accordance with the ISO 5167 standard and generate only low residual pressure loss.
Medium | Steam |
Flow Velocity | 14 m/s |
Density | 17.8 kg/m³ |
Pressure | 56 bar |
Temperature | +450°C |
Being a main instrumentation vendor (MIV) with many years of industrial experience in the power plant sector as well as in custody transfer and billing applications, KROHNE was able to qualify as a partner on this project. KROHNE supplied a complete solution consisting of flow, pressure, and temperature measurement devices as well as a flow computer. This package also included design and sizing, as well as documentation and calibration in accordance with the Dutch Power and Heat Act. The complete package focused on the following four measuring points:
For feedwater measurement, KROHNE supplied the OPTISONIC 3400 ultrasonic flowmeter with a remote field-mounted signal converter (F). The measuring device monitors the amount of feedwater used for the biomass-fired steam boiler. The OPTIBAR PM 3050 pressure transmitter and the OPTITEMP TRA-S34 temperature assembly were also installed. This enables the energy content (enthalpy) of the feedwater to be determined in addition to the volume flow.
The readings are then transmitted to the SUMMIT 8800 flow computer. The measured values serve as important parameters for adjusting performance of the plant as required. In addition, they evidence the amount of feedwater used for cogeneration and enable clear-cut separation from the process of the conventionally fired auxiliary boiler.
To enable the operator to bill the process steam quantities used, KROHNE supplied a measuring section calibrated according to ISO 5167. This consists of a Venturi nozzle with annular chamber as primary element, including a forged 5-way manifold and process valves. The flow rate is measured by the OPTIBAR DP 7060 differential pressure transmitter. In this application it has a differential pressure measuring range of up to 500 mbar with overload protection up to 160 bar.
KROHNE carried out calibration on a traceable calibration facility using the same Reynolds numbers prevailing in the real process. The OPTIBAR DP 7060 was also 3D-linearised at the factory over the entire range of static pressure and ambient temperature. As a rule, high line pressures and increased ambient temperatures have thus practically no influence on the measurement uncertainty. In addition, the measuring point was equipped with the OPTIBAR PM 3050 pressure transmitter for gauge pressure measurement as well as the OPTITEMP TRA-S34 temperature assembly. This enables the operator to carry out a pressure and temperature-compensated mass measurement and additionally determine the thermal energy (enthalpy). All measured values are transmitted to the SUMMIT 8800 flow computer approved for custody transfer measurements.
#1 Feedwater measurement #2 Process steam flow measurement #3 Steam flow measurement to back-pressure turbine #4 Feed-in measurement of steam for district heating network
Calibrated measuring section with Venturi nozzle, OPTIBAR DP 7060, OPTIBAR PM 3050 and OPTITEMP TRA-S34
Another traceably calibrated measuring section with the same instrumentation was installed in the steam line supplying the back-pressure turbine. All measured values are again processed by the SUMMIT 8800. The energy quantity of this measuring point is offset against the energy quantity of the previous measuring point so that the individual steam flows can be recorded exactly separated from each other.
In order to bill the energy fed into the district heating network, the existing flow measurement into the turbine is combined with the enthalpy measured at this point. The measuring point is equipped with the OPTIBAR PM 3050 pressure transmitter and the OPTITEMP TRA-S34 temperature assembly. The SUMMIT 8800 calculates the energy with the flow measurement readings of the turbine feed and precisely determines the energy flow to the district heating network.
Installation of Venturi nozzle
Temperature measurement with the OPTITEMP TRA-S34
The traceably calibrated measuring sections reduce the installation effects on measurement to a minimum so that the energy flows are measured accurately and in accordance with the legal requirements. In this way, the operator complies with all requirements, both for the billing of steam quantities and for state subsidies and feed-in tariffs.
In addition to the measuring sections and the associated instrumentation, KROHNE supplied the full scope of services required – from engineering, documentation and material certification to calibration and commissioning on site. Here Stork Thermeq and the operating company benefited equally from a comprehensive tailored solution, which KROHNE was able to deliver from a single source thanks to its process knowledge and years of experience in custody transfer and calibration.
KROHNE is able to provide the appropriate flowmeter technology for all Power and Heat Act-related applications. This includes applications such as steam, feedwater, condensate, fuel gas, etc.,
e.g. measurements in district heating networks according to MID MI-004 (accuracy class 1).