BM Retrofit DEMO Kreuzstetten

This demo is part of the BM Retrofit project that has been completed. Download the BM Retrofit Publishable Final Report here.

The Kreuzstetten demonstration project is a medium-sized, biomass-based district heating network that supplies approximately 160 customers via an 8,700-meter-long pipeline and has an annual heat demand of about 5.5 GWh. The plant consists of two biomass boilers, each with a capacity of 1 MWth, a 40 m³ buffer storage tank, and an 88.5 kWp photovoltaic system. The biomass boilers are oversized for the heat demand, as a significant increase in the number of customers was expected but did not materialize. This poses a challenge for the operation of the biomass boilers, as they regularly run in partial-load operation with reduced efficiency and must frequently be shut down and restarted. Another challenge is a pumpkin seed dryer that requires a very high peak load for a short period of time. Among the main problems were a low summer load, which led to increased heat losses, as well as inefficient operation of the biomass boilers. In addition, temperatures in the district heating network were relatively high and had to be lowered.

In the BM Retrofit project, the potential for optimisation was examined in detail and in a structured manner. Modern and sustainable modernisation concepts were developed for Kreuzstetten in the form of a retrofit. The measures developed were tested and validated at the Kreuzstetten biomass heating plant to ensure that they can be quickly replicated in practice, so that the findings can be applied to other sites in the future.

Objective of the BM Retrofit Kreuzstetten project

The BM Retrofit project in Kreuzstetten pursued several objectives in order to exploit the optimisation potential of the biomass heating plant. The project also aimed to expand and densify the network.

What was the goal? On the one hand, the control and operation of the biomass boilers and the entire heating network should be improved, especially in summer. On the other hand, the control and operation of a large consumer that needs the heat produced in Kreuzstetten for its drying plant for agricultural products (including pumpkin seeds) should be optimised. Furthermore, the integration potential of heat pump systems and absorption heat pump systems should be investigated.

Approach and methodology of the BM Retrofit Kreuzstetten project

At the start of the project, a comprehensive analysis of the district heating system in Kreuzstetten was conducted. The analysis revealed that an extremely low summer load, accompanied by correspondingly high heat losses of up to 65%, poses a major challenge. During this period, the biomass boilers (2 x 1 MWth) operate at less than 20% of their rated load, forcing them into stop-and-go operation.

In parallel with the measures taken on the generation side, a network optimization was carried out. A detailed analysis on the consumption side identified open bypass flows and suboptimal heat exchanger settings as the main causes of high return temperatures. Through targeted optimization of the substations and elimination of the bypass flows, the average network return temperature was lowered from 55–60°C to 40–45°C, corresponding to a reduction of approximately 15°C. As a result, the temperature difference between the supply and return increased by about 13°C, leading to a reduction in the specific volume flow of 13 m³/MWh of heat supplied. This reduced the power consumption of the network pumps by about one-third. These improvements directly increased the overall system efficiency and lowered operating costs.

In addition to plant operations, the district heating network was analyzed to assess its current condition in terms of temperature loads, pressure loads, and bottlenecks. This data was used for thermohydraulic simulations.

Iterative improvements to buffer management led to a significant reduction in start-up and shutdown cycles. Given the relatively large size of the biomass boilers, the improvement is most evident in the utilization of the buffer volume when analyzing the temperature profiles in the buffer tank. Here, the temperature profiles prior to the improvement showed low utilization of the buffer storage tank in order to avoid strong modulations and start-up and shutdown cycles of the biomass boiler. Following the improvement in buffer management, the temperature profiles show full utilization of the installed buffer volume. This means that the potential for improvement through rule-based buffer management has been fully realized.

To address the inefficient summer operation of biomass boilers, a summer solution based on an air-source heat pump was investigated. Various heat pump capacities ranging from 300 to 400 kWth were analyzed. The simulation results show that a 300-kWth heat pump could cover summer demand from early May to mid-September, which corresponds to approximately 13% of the annual heat demand.

In summary, the BM Retrofit project at the Kreuzstetten site was investigating how a holistic optimisation of the local heating network can be achieved. Other biomass heating plants can also optimise their plant operation on the basis of these findings.

Profile of the BM Retrofit DEMO Kreuzstetten project. Click on the image to download the PDF (german only)!

Links:

• Flagship Project BM Retrofit
• Report Insight Talk Innovative Heating Solutions
• BM Retrofit solutions for heating network operators >> information sheet (german only)
• BM Retrofit solutions >> optimised display for mobile phones (german only)