NO. 4 /2019
INTERNATIONAL MAGAZINE ON DISTRICT HEATING AND COOLING
SECURE THE ASSET IN YOUR DISTRICT HEATING NETWORK
NEW THERMAL HEAT STORAGE IN GREATER COPENHAGEN
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DBDH Promoting District Energy for a Sustainable City transformation
THE COLUMN CRUNCH TIME By Birger Lauersen, Manager International Affairs, Danish District Heating Association and Vice President, Euroheat & Power
FOCUS FROM COMPONENT TO SERVICE – AN IOT JOURNEY THAT HAS ONLY JUST BEGUN By Martin Overbjerg, Business Development Manager, District Energy, Frese A/S
FOCUS SECURE THE ASSET IN YOUR DISTRICT HEATING NETWORK By Peter Jorsal, Product & Academy Manager, LOGSTOR A/S
FOCUS WHY IMPROVE THE WATER QUALITY IN DISTRICT HEATING SYSTEMS? By Thomas Dalsgaard, Head of Sales, SILHORKO-EUROWATER A/S
FOCUS NEW THERMAL HEAT STORAGE IN GREATER COPENHAGEN By Finn Bruus, team leader, VEKS and Per Alex Sørensen PlanEnergi
FOCUS BIOMASS BOILER TO NEW PLANT IN FRANCE By Jens Dall, Managing Director, Dall Energy
FOCUS FROM SEASONAL TO SMART ENERGY STORAGE By Alfred Heller, Managing Consultant, NIRAS
EXPANSION OF INNOVATIVE COPENHAGEN DISTRICT HEATING PROJECT By Christer Frennfelt, Business Development Manager, Consultant & Utility, SWEP
BRINGING CLEANER HEAT TO THE WORLD’S COLDEST CAPITAL, ULAANBAATAR By Greg Gebrail, Sector Specialist – District Energy, European Bank for Reconstruction and Development; Andrew T. Christensen, Chief Specialist, Energy, COWI A/S; and Anton Dan-Chin-Iu, Principal Banker, European Bank for Reconstruction and Development (EBRD)
MEMBER COMPANY PROFILE: ALBERTSLUND DISTRICT HEATING COMPANY
Front page: The Dall Energy heat & power plant in Sindal, Denmark.
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D I S T R I CT ENERGY - SUS TA I NAB L E C I T Y T RANS FORMAT I ON
The future is knocking, in the shape of Brunata’s new network-based technology, which not only provides a stream of precise consumption and property data, but also gives opportunities for energy efficient, environmentally friendly and resident oriented solutions. All meters connect to Brunata’s Internet of Things, which can be expanded with countless other solutions such as garbage sensors, light sensors, smoke sensors and much more. Read more at brunata.com
By Birger Lauersen, Manager International Affairs, Danish District Heating Association and Vice President, Euroheat & Power
Crunch – time
that district heating and cooling (DHC) can make to the energy transition - to von der Leyen’s “Green Deal”.
Urbandictionary.com defines “crunch time” as: “The interval of time immediately before a project is due, when it becomes apparent that the schedule has slipped, and everyone is going to have to work like dogs to try to complete the project in time.” Have we arrived at crunch time with regard to our efforts to combat climate change? We are certainly in a situation where the European political system is facing the fact that the pressure to deliver on the green transition increases and it’s getting increasingly difficult to kick the can down the road. Promises to deliver have been made, but not met, and a spectrum of organizations and people, stretching from Extinction Rebellion, over Fridays for Future, with Greta Thunberg, to ordinary voters, are increasingly vocal in their demands for action. It is apparent that the timetable has slipped, and we are going to work like dogs to make up for it. That is also the new reality in European politics. The election in May to the new European Parliament brought together a greener assembly, and the European Commission President Elect, Ursula von der Leyen had to commit to proposing a new “Green Deal”, with raised ambitions, within 100 days. This is the reality in which we, the European district heating and cooling sector, will have to find our place. Fortunately, it isn’t hard. Many European cities are working on delivering “a green deal” to their citizens. They have realized that heat is and will remain the dominating demand for energy services. And heating absolutely needs both higher efficiency and a transition to renewable energy. Cities cannot do much about the composition of Europe’s electricity supply or the fuel use in transportation, but they can do something about the heat demand in their city. That’s why we, as a sector, are teaming up with cities in enhancing the understanding that EU stakeholders, the Commissions, Parliament and others, have of the contribution
And cities want to team up with us. But only if we as a sector commit to develop, so that our networks continue to grow smarter, more efficient and better integrated with the wider energy system to help facilitate the overall transition to a decarbonized, more resource efficient and better integrated into the circular economy. We must also strive to evolve together with the needs of our customers, to provide the best possible user experience and let ourselves be guided by the fundamental principles that matters to our cities: fairness, social responsibility and transparency. I’m therefore proud that the European sector, represented by Euroheat & Power - The European association for DHC - offers its commitment to do exactly that. The European DHC Community Decarbonisation Pledge was presented at an event in Brussels on October 1st. And I’m particularly proud of the support this pledge has received by cities all over Europe. A number of mayors of European cities, from Kozani in Greece to Oslo in Norway – from Amiens in France to Võry in Estonia, have given testament to how important DHC is in their efforts to become sustainable. See them at https://www.euroheat. org/vision2050/ This commitment is also a call on the sector that provides services and hardware for the DHC sector. Everybody must be prepared. Not only to deliver more products and services in response to the increased demand for these, which we believe will occur in the coming years, but also to respond to the demand for new and innovative solutions needed to facilitate the growth of DHC in cities outside the traditional DHC countries. I’m confident that the entire DHC industry - utilities, manufacturers, service providers and others – are ready to meet the challenge here at crunch time.
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20% of energy saving potential using hydronic balancing controls
Virtus. Shaped for the future
Optimal hydronic balance and perfect temperature control is the key to maximizing efficiency of heating and cooling networks. With that it also means that you are saving energy, money and improving end-users’ comfort. To help achieve your goals, Danfoss developed a new range of heavy duty differential pressure and flow controllers for most demanding district heating and cooling applications, named Virtus. iSET function implemented in differential pressure controller will enable additional optimization of your district heating/cooling substation operation. Danfoss’ new ready pressure and flow controllers with intelligent iSET function
To find out more visit virtus.danfoss.com
By Martin Overbjerg, Business Development Manager, District Energy, Frese A/S
– an IoT journey that has only just begun
The future is service based. A point that major software developers have been aware of for some time, and a principle which several of them have now built their business models on. Microsoft has done it with their Office package, Adobe with Creative Cloud. The concept is Software as a Service (SAAS). And, as consumers, we have gotten used to that concept. But in the district energy sector it is a fairly new mindset. Historically, the industry that supports district energy has delivered components such as pipes, valves and pumps. Quality components that the customer bought and then owned and maintained.
Frese thus began a journey from hardcore manufacturer of brass components to future service provider. An IoT journey towards delivering remote flow control as a service. The development of the Flowguard had begun. TWO-WAY COMMUNICATION – ON BATTERIES? The basis for the new IoT component was already in place: A 2nd generation pressure independent control valve, which regulates flow and temperature in heating and cooling applications and combines an externally adjustable automatic balancing valve, a differential pressure control valve and a full authority modulating control valve in one compact valve housing.
But two years ago, an opportunity presented itself.
CUSTOMER DRIVEN INNOVATION A customer, Naestved District Heating Company, had a need for a battery-operated valve solution, which would allow them to remotely monitor, operate and shut down the flow in individual heat interface units. The solution should be independent of the customer’s electrical and internet installations and should not depend on a SIM card and must be retrofitted into existing heat interface units. The main purpose was to be able to not only monitor, but also operate the valves right down to household level, remotely, thereby saving district energy operators man-hours in daily operations or in case of interruptions. Target installations would primarily be apartment blocks with several apartments and HIUs (heat interface units), where tenants are required to be present when technicians arrive to check and adjust the valve. With an IoT (Internet of Things) solution, neither tenant nor technician needs to be in the vicinity of the HIU, if adjustments are necessary. This saves money and improves customer service. The solution also needed to be low-cost and easy to install, given the number of individual HIU’s that a district energy operator like Naestved Fjernvarme (Naestved District Heating Company) owns.
With an IoT Bypass solution, district energy operators can monitor pressure and reduce unnecessary heat loss in their network, and thereby save energy.
While remote monitoring was already a well-known technology found in heat meters, which provide district heating companies with information but cannot perform an active task, it would be necessary to establish two-way communication in order to actually operate the valves remotely. The required independence of internet connections and mobile phone technology meant that an alternative solution had to be found, but the biggest challenge was to make the component battery operated, and, above all, to ensure long battery life.
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The intelligent and controllable bypass solution will enable the district energy operator to reduce the temperature in the network, improve pump efficiency and save energy. Providing temperature control and several pressure measurements, it is built on exactly the same principles as the Flowguard – battery operated with LPWAN technology, and easily retrofitted into existing bypass units and substations. Again, the need for a battery-operated solution complicated the development process. The traditional mechanical thermostats you find in a bypass had to be replaced by an electronic one – once again with minimal use of battery power. Developing this thermostat was a difficult and time-consuming task, which required close cooperation with friends in the district energy sector.
It became clear that the controller only needed to transmit very small data packages regarding operational conditions and receive even smaller data packages in order to control the flow, and only at certain intervals. This is in fact the case with many IoT solutions. This meant that narrowband technology (LPWAN) would be ideal for our purposes, and as the Sigfox network specializes in IoT solutions with many devices spread over a large geographic area with limited and infrequent message needs, it was the logical choice. 10-YEAR BATTERY LIFE The original intent was to use a pressure independent control valve with 5.0 mm stroke due to its high flow capacity. However, it soon became clear that this stroke length would place much too high a strain on battery life. It was replaced by a 2.5 mm stroke valve, which meant a trade-off where high precision - which is not crucial in this solution – was partly sacrificed for long battery life. Another draw on battery life would usually be the actuator, but since the controller is more or less an open or close component, and since the valve only draws battery from it, when it is in motion, the motoric actuator for the PICV (pressure independent control valve) will have very low impact on battery life. With the narrowband technology combined with a short stoke valve and ultra-low consumption by the actuator, it was possible to generate a battery life on the controller of up to 10 years, while keeping the device small and discreet enough that it can easily be retrofitted into the consumers’ existing heat interface units. Now, two years later, Naestved Fjernvarme has installed 200 IoT units, and has shared valuable experiences about the installation process, which will benefit other district heating operators. IoT solutions will save manpower in the long run, but companies still need to gain access to the HIU’s to install them. However, as Naestved Fjernvarme was quick to discover, much preparation can take place in their own workshop, thereby limiting the time that technicians must spend in the field. The company is now about to start analyzing all the new available data. BYPASS IOT CAN IMPROVE EFFICIENCY One thing often leads to the next, and it soon made sense to turn the first IoT product into an IoT Bypass solution which allows district energy operators to monitor their network and ensure that the pipeline is kept warm during the non-heating season. Most installations today are static and non-controllable, which leads to unnecessary heat loss from the district heating network.
However, after months of trial and error, this IoT bypass solution now has an expected battery life of up to five years.
A district energy network with two-way IoT communication.
CLOUD-BASED SOLUTION Information is worthless unless you can access and analyze it. Therefore, these new IoT components are monitored and operated via a cloud-based dashboard, the Flowcloud, which will provide district energy operators with one central access point to all units from their desk at the office or while they are in the field via a mobile phone or tablet. The solution has also been designed for maximum flexibility regarding operational data via API’s to third party control systems. Some complex IoT solutions tend to be quite proprietary, but the approach should be that the data belongs to the customer. We are very happy to offer them a platform solution, which is easy and simple to operate, if they do not have a large setup. Have they already gone into digitalization and built up a platform, then of course that is where data must be provided, adding value for the district energy operator.
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Another key point is data sharing, which will only accelerate as district energy and other utility companies start reaching for further optimization and synergies. PERSPECTIVES With the international agenda focused on climate change and the reduction of CO 2 emissions, the Danish district energy sector has set ambitious goals. Optimizing technology and operations is one of the key elements in reaching them. While infrastructure projects are often complex and expensive, there are lower-hanging fruits ripe for the picking. By integrating and retrofitting IoT-based components into existing systems, you can obtain energy savings, as well as lower costs for district energy providers and consumers, with relatively low startup expenses and stable operational costs. It is a journey that requires a new mindset. At Frese, we are picking up the pace.
WHAT IS SIGFOX? The Sigfox network is a Low-Power Wide-Area Network (LPWAN), which utilizes narrowband technology. Where Wi-Fi and mobile phone technology lets us send and receive large amounts of data almost instantly, Sigfox can only transmit very small data packages of 12 bytes and receive 8 bytes. This, however, is enough for many IoT products. Because the data packages are so small, and because the units only need to transmit and receive data at certain intervals, they consume very little electricity. This allows them to be battery-operated. Narrowband technology also has very long range and can cover a wide area, so the controller can easily transmit data to a base station several miles away without losing power. Another benefit of using Sigfox is that it is not based on the mobile phone network. This means that the unit needs no sim card but only an integrated chip, which makes it much less complicated. This solution is very easy to install, deploy and operate. The necessary infrastructure is already in place, so there is no need to establish new networks. It is as close to plug- and-play as you can get, with full financial transparency and predictability, ensured by a fixed subscription rate per unit.
For further information please contact: Martin Overbjerg, firstname.lastname@example.org
THE ENERGY SYSTEM OF TOMORROW
A new generation of energy storage from Arcon-Sunmark levels production and provides flexibility all year long. Large-scale energy storage systems are in demand, and for good reason. They make it possible to collect waste heat, surplus energy from wind- and PV farms, solar thermal produced energy and use it whenever it is needed. Also large CHP plants will benefit from this, as it makes it possible to decouple production from heat demand. Energy storage with hot water, called Pit Thermal Energy Storage (PTES) – and used in large scale solar plants – was one of the first of its kind. Now a new generation developed by Arcon-Sunmark in Denmark is arriving. The new generation deals effectively with the challenges from the previous one and comes with a: • Top that is divided into sections for intelligent leakage control • Well with pumps in each section to handle water on the surface • Controlled layer of ballast that keeps the lid in place • Well-insulated lid that minimizes the heat loss from the storage These features – and more – add up to a new performance standard as well as a new level of flexibility all year long.
A new generation of thermal energy storage has been developed by Arcon-Sunmark. It brings PTES to a new standard.
For further information, please contact: email@example.com
Arcon-Sunmark AS is an international expert in the solar heating sector and supplies everything from solar collectors to large turn-key solar heating systems. Arcon-Sunmark is owned by VKR Holding A/S who invests in companies that bring daylight, fresh air and better environment into people’s everyday life. In total, VKR Holding A/S employs 16.000 people in 41 countries.
By Peter Jorsal, Product & Academy Manager, LOGSTOR A/S
Asset management has become a popular concept within district heating in recent years. It deals with securing the value of your district heating network and production plant. In other words, it is about ensuring that as a minimum you obtain the expected service life with a minimum of operational stoppages and maintenance costs. Asset management often concerns the period after systems have been put into operation. This article will mainly address what you can do in the planning phase to secure the value of your district heating network, but also what you can do in the construction phase and operation period.
Weld joints require more installation equipment, but they also make it possible for the energy company to make person- independent requirements as regards weld data input, where data is scanned from a QR code on the casing joint, as well as requirements to the documentation of the welding process. A lot of development work is being done to make the tool part of weld joints more accessible to a major number of contractors, which will obviously increase the part of weld joints in future district heating networks. See below example of a press tool with an air pressure, which can be used for all dimensions in range ø 225-800 mm as well as the example of the vital weld process documentation.
NEW DISTRICT HEATNG SYSTEMS: PLANNING
Design The correct design, as regards the operational conditions (temperatures, pressures, variations etc.), that the system will be exposed to is decisive for the service life. Movements and stresses must be addressed, and the best solution is to use as few components as possible and avoid the use of operational compensators altogether in order to extend service life. The pipe supplier has great experience with the design of district heating (DH) systems and should be involved together with the consultant. Choice of casing joint History shows that system damages typically arise in casing joint systems, and the majority is due to faulty installations. In relation to asset management, the choice of casing joint system is essential to make sure the system will have the service life you expect, and that you do not incur unforeseen repair expenses. Thus, it is vital to choose a casing joint system with a documented service life like this for the rest of the pipe system. The casing joints must also be easy to install in order to minimize the risk of faults, and it must also be possible to test the installed casing joint to ascertain whether the installation is correct or not. History has taught us that the best choice is between the following casing joint types: • Shrinkable cross-linked PEX casing joints, sealed with mastic • Weld joints, fusion-welded to the outer casing of the pipe
CHOICE OF SURVEILLANCE SYSTEM Establishing a well-functioning surveillance system is decisive for due information about and localization of any damage, where moisture enters the PUR insulation. In this way it is possible to repair the damage before it spreads, and make sure that the damage does not affect the expected service life of the pre-insulated pipe system. So, the surveillance system is a crucial tool in the asset management. The surveillance system must ensure that the following faults are quickly reported: • Weld faults • Installation faults, casing joint installation • Product faults • Excavation damages • Steel fatigue • Any corrosion on the service pipe
Weld joints are considered by the market to be the best, but at the same time the most expensive joint solution.
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The basic function of the surveillance system is to report when moisture has entered the insulation and show how the fault has developed over time. Surveillance systems can be designed after very different principles: • Passive system. Manual measurements of the system by a measuring technician at set intervals e.g. once or twice a year. No active surveillance of the system between these measurements. Fault location, if any, is done by the measuring technician. • Active system based on the resistance measuring principle with information about whether there is moisture in the insulation or not. Further analyses of the insulation resistance values and galvanic voltage can be performed to establish whether the insulation is wet or dry and whether any moisture enters from the service pipe or from the outside. Fault location, if any, is done by the measuring technician. • Active system based on the impedance principle. In addition to above possibilities, the system can locate any fault in the system. As regards asset management the recommendation obviously is to establish an active surveillance system, which makes it possible continuously to monitor and analyze the condition of the pipe system. This enables due intervention as regards any damage before it evolves and spreads in the system. In this way, the surveillance system forms the basis for obtaining at least the expected service life at a minimum of costs. REQUIREMENTS TO CONTRACTORS Even if the products are of the highest quality, if the installation is not carried out according to the instructions, the system will not be faultless, and repairs will be necessary. It is therefore important to make requirements to the contractor prior to the installation. For the pre-insulated system, the welding of the steel pipes and the installation of casing joints are decisive for a faultless system during the operational period. For many years, there have been very well-defined requirements to steel welds, and it is a tradition to prescribe these. For the installation of casing joints, it ought to be a fundamental requirement that the fitters are trained to do so, but this is not always the case. In fact, they often have no training in installing these. The energy companies ought to require that casing joint fitters have attended a course at the pipe supplier’s and have been certified at regular intervals to install the casing joint type in question. In addition, the energy company should require that the course gives the fitter a theoretical as well as a practical training in installing the relevant casing joints. It would be a big step for the DH trade to raise the requirement to casing joint installation to the same level as the requirement to steel welds.
As for the surveillance system, an uncertainty often exists about the acceptance criteria for the finished system. It is recommended to require that the acceptance criteria for the insulation resistance in the surveillance system follow the specifications of the supplier of the pre-insulated pipe system. The contractor must then document this on handover, and it will be a precondition for a good starting point in the asset management during the operational period. Most faults appear by far in the first years after putting the system into operation. With an active and well-functioning surveillance system these faults will be found within the guarantee period of the supplier and contractor, and in this way the energy company ensures that there is a sponsor for repairing the damages. NEW PIPE SYSTEMS: THE CONSTRUCTION PHASE Trust is good, but control is necessary. It is decisive for the pre- insulated pipe system being installed without built-in faults after the instructions that an active inspection is performed in the construction phase. Unfortunately, this is often neglected. With an active supervision, potential faults are stopped in due time, and the basis for a faultless system for the part of the asset management belonging to the operational period will be good. It is therefore recommended that the energy company is trained to supervise casing joint installation and surveillance systems at the pipe supplier’s. OPERATIONAL PERIOD In established district heating networks, the active surveillance system must be monitored continuously, and you must react to the information you receive. The energy company can monitor the surveillance system, but it is also possible for the pipe supplier to offer this service.
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The only physical thing you can see in the pre-insulated, buried system are the pre-insulated valves in chambers. The energy company should establish a routine for planned chamber inspections 1-2 times a year, where the valves are operated. This ensures a long service life of the pre-insulated valves. In addition, it is possible to install detectors in chambers, which sends a message if the chamber is flooded.
OLD PRE-INSULATED PIPE SYSTEMS WITHOUT SURVEILLANCE SYSTEM AND PIPE SYSTEM IN CONCRETE DUCTS
In these systems, the only way to monitor the condition is to make thermographic surveillance as periodic inspections of the DH networks. If there are leaks in the steel pipes with major water loss, then it is also possible to locate the area where the leak is by analyzing data from meters in the system and at consumers’. In these systems, damages are not found until they are comprehensive e.g. moisture coming from the outside and spreading in the system or an actual rupture of the steel pipes with water loss as a result. In old systems with surveillance wires, it will therefore be much preferable to update the system to an active surveillance system, so you can always react quickly, before the faults evolve to large and expensive damages. DIGITALIZATION AND FUTURE DEVELOPMENT The trend is towards the energy companies wanting more and more data from the systems. Data, from which they can make the right choices. This is also true of pre-insulated pipe systems, and we will certainly see a trend towards more ”digitized” pre- insulated pipe systems.
EXISTING SYSTEMS In many pre-insulated pipe systems with a surveillance system that has been in operation in a few or many years, the surveillance system is often not up-to-date regarding drawing material and it is often a passive system. It is recommended to update the drawing material and make precise, as-built drawings, and then upgrade the surveillance systems to active, continuously monitored surveillance systems. This is possible for skilled measuring technicians and will certainly extend the service life of the pre-insulated pipe system instead of continuing with the “old” one, because then it is possible to repair old faults and respond quickly to new ones. In old pre-insulated pipe systems, there is often a problem with leaky casing joints, which can be located with an updated surveillance system. It is recommended to make a renovation plan for exchanging old leaky casing joints, because it will prevent further corrosion of steel pipes and leakages in the pipe system. There are products and techniques available to replace old straight joints, bend joints and T-joints without interrupting the operation and cutting the steel pipes. It requires a special installation technique and trained fitters.
For further information please contact: Peter Jorsal, firstname.lastname@example.org
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By Thomas Dalsgaard, Head of Sales, SILHORKO-EUROWATER A/S
Demineralization and deaeration of district heating make- up water have for many years been a privilege for only a few major district heating companies. Lately it has become possible for smaller and middle-sized district heating companies to benefit from new technologies to produce salt and oxygen free district heating water. WHY IS IT IMPORTANT TO REMOVE SALTS AND OXYGEN IN DISTRICT HEATING MAKE-UP WATER? Often smaller district heating (DH) companies argue that “we have always used softened make-up water. We add chemicals for alkalizing the water, scavenging oxygen and then take care of hard water that eventually breaks into our system”. Another common statement is that “when we cut our pipes we see no corrosion. If we see corrosion it must be coming from outside the pipes”. The last postulate might very well be the first impression you get when you look on a corroded pipe, but it is not always the reality.
WHAT CAUSES CORROSION AND CAN CHEMICALS AVOID CORROSION? There are four main factors promoting corrosion; • Aggressive ions (salts) causing increased conductivity in the water • Oxygen • Incorrect pH • Biological activity The corrosion process has started from the inside of the pipe and penetrated the steel. Water will leak to the outside of the pipe, and the corrosion process will proceed and accelerate continuously as long as the conditions for corrosion exist. Corrosion products will continue to form outside the pipe, growing bigger and bigger corrosion products. The corrosion products shown on the picture have grown so big that it has lifted the insulating layer of polyethylene (PUR), creating an air gap between the steel pipe and the insulation.
Example of corrosion in a district heating pipe. At first it might look like the corrosion is coming from the outside penetrating to the inside but typically it’s not the case.
The photos show corrosion on a DH pipe due to poor DH water quality. High content of salts, and the presence of oxygen has started the corrosion process inside the DH pipe.
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Corrosion is an electrochemical reaction between oxygen, water and metal. The reaction can only happen if all three components are present. Therefore, make-up water should ideally be demineralized, deaerated and pH adjusted.
Salts and oxygen serve as catalysts for corrosion. Salts increase the conductivity in water, which is a prerequisite for corrosion, and the oxygen oxidises (combines with metal ions to form rust) and corrodes the steel in the DH pipe. Due to these processes, the use of chemicals in DH systems should be reduced as much as possible because they increase the salt content and thereby the conductivity of the water circulating in the system. Another issue with the chemicals used in DH systems is that they are often organic chemicals, which, if added to the water will serve as nutrients for bacteria growth and formation of biofilm, leading to biocorrosion below the film. They also form sludge and increase the risk of deposits, which typically occur in places where the water velocity is low, e.g. in heat and accumulation tanks. The bottoms of the tanks can suffer from severe corrosion due to deposits and sludge. Finally, it should be mentioned that the best oxygen scavenging agent in the system is the steel surface. If steel and oxygen scavenging chemicals compete for the oxygen, the steel surface always wins. If water contains oxygen the corrosion process will continue. If there is no oxygen the corrosion process will cease. At low pH values, the corrosion process increases, and at high pH values, the risk of corrosion in copper, copper alloys and metal parts of aluminum and galvanized parts also increases. The recommended pH of DH water is 9.8 ± 0.2, and this should be achieved by dosing sodium hydroxide (NaOH). When demineralized water is used in the system, the amount of NaOH will be reduced dramatically, whereas the use of softened water calls for high use of NaOH due to its content of carbonate. NEW MODERN WATER TREATMENT TECHNOLOGIES - WITHOUT USING CHEMICALS Natural drinking water is characterized by having a balanced content of cations and anions. All together these make up the total hardness, salts and gasses like oxygen (O2), carbon dioxide (CO2) and nitrogen (N2). For removal of hardness and salts the most common water treatment technologies are: • Water softening, which removes the total hardness from water. • Demineralization of water by use of reverse osmosis or ion exchange. • Production of ultra-pure water where the remaining salts are removed, sometimes referred to as polishing.
Example of water treatment steps – from ground water to pure water.
As mentioned, it is very important to remove salts and oxygen because they are prerequisites for corrosion. Furthermore carbon-dioxide should be removed since it increases the conductivity and the consumption of NaOH (lye). Therefore, gasses like oxygen and carbon dioxide should be removed before thewater is used asmake-upwater. In case oxygen enters the district heating system through leakages, the character of corrosion will change from aggressive local corrosion to general surface corrosion, which is not as critical as local corrosion. New efficient technologies have made degassing an attainable solution for all district heating companies. The recommended solution is a Membrane Degassing Unit (MDU). It should be said than an MDU can be used to degas softened water, but the superior result will be achieved using demineralized water.
Example of a MDU plant (Membrane Degassing Unit).
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OVERVIEW: ADVANTAGES OF USING DEMINERALIZED AND DEAERATED MAKE-UP WATER IN DISTRICT HEATING SYSTEMS • The risk of corrosion is reduced because the corrosion process requires salts and oxygen to react. • By reducing the salt content in the water, the risk of microbiological growth in the district heating system is reduced, which again reduces the risk of microbiological corrosion. • The need for chemicals is significantly reduced (typically more than 90%) because the “buffer” in the water is reduced by reducing the salt content. The “buffer” defines how much NaOH is needed to change the pH. Water with a low buffer gets effected by NaOH more easily than water with high buffer. Therefore, less chemicals are needed for demineralized water than just softened water. • Using demineralized water in the district heating system makes detection of raw water break-in much more efficient
Demineralization and deaereation plant at Aars District Heating. The complete make-up water treatment plant consists of a water softener plant, a reverse osmosis unit (RO), a membrane degassing unit (MDU) and a dosing station for dosing NaOH. The RO and MDU units are shown here.
than in systems with just softened water. This is because raw water break-in into demineralized water creates bigger fluctuations in the parameters of the system. • By using demineralized water with low conductivity instead of softened water, the corrosion which will occur when raw water breaks into the system will be the relatively unharmful general surface corrosion instead of aggressive local corrosion. • An MDU-plant removes oxygen and carbon dioxide in the demineralized water by means of membrane contactors, a vacuum pump and nitrogen as a sweep gas. This method is very efficient and reduces the oxygen content in the demineralized make-up water from 5-10 mg O2/liter to below 0.02 mg O2/liter.
GRAPH 1: CORRELATION BETWEEN PH, CONDUCTIVITY AND SALTS
CASE STUDY: PRACTICAL EXPERIENCE WITH IMPROVING THE WATER QUALITY IN A DISTRICT HEATING SYSTEM. Aars District Heating Company is a CHP plant that produces and distributes electricity and heat for about 5500 households. Heat is transmitted through one transmission line to 6 distribution networks. The make-up water was previously produced in a water softener and deaerated in a traditional vacuum deaerator. In July 2018, the water treatment strategy was changed. Today the make-up water is demineralized. The make-up water is produced in a central water treatment plant, and all make-up water is added to the transmission line. All distribution networks get their make-up water from the transmission net. Since then the use for oxygen scavenging chemicals has been eliminated completely. In addition, the use for chemicals for pH adjustment has been reduced 95%.
Graph 1 shows the development in the water quality in the transmission line in the period July 2018 to October 2019. In this period, the water quality has changed from softened water to demineralized water. Thus it follows the “Recommendations for Water Treatment and Corrosion Prevention”, authored by the Danish District Heating organization. In the beginning of January 2019, a system leak occurred and as an emergency, soft water with higher conductivity was used as additional make-up water. This can be seen as the increased content of chloride, sulfate and conductivity. A slight increase in the content of sulfate can be seen October 2019. A possible explanation for this is that sulphate reducing bacteria had been reduced due to the improved water quality. The reason is that harmful bacteria simply do not get any nutrients (salts) to support life. Therefore, the bacteria do not any longer “eat” the sulphate. This explanation is supported by measurements in the content of sulphide (not shown on the graph). In the beginning of the period the level of sulphide was 0.5 mg/l but in October 2019 it was reduced to below the detection limit.
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SUMMARY Optimum water treatment will help prolong the lifetime of pipes and critical components in the DH system. By desalination, deaeration and pH adjustment, the lifetime increases. Consider a business case where the lifetime of the pipes was increased from 50 to 70 years. The important measures to avoid corrosion are: • Reduce the conductivity in DH water by use of demineralized water and keep oxygen out of the system. Salts and oxygen are powerful catalysts for corrosion. • Avoid unnecessary use of chemicals. Chemically speaking, oxygen reacts faster with steel than oxygen binding agents. Chemicals also increase the conductivity, the risk of forming sludge and they act as nutrients for corrosive microbiological growth.
GRAPH 2: CORRELATION BETWEEN PH, CONDUCTIVITY AND SALTS
The above graph for one of the distribution networks clearly shows problems with raw water break-in. This clearly occurs in the period from April to the beginning of July 2019, where chloride, sulphate and conductivity increases while the pH value slightly decreases. After this period the leakage stopped, and the parameters returned to normal.
For further information please contact: Thomas Dalsgaard, email@example.com
NIRAS Energy Private as well as public investors prefer NIRAS’ international experience within district heating and biogas plants. This applies to both renovation of existing plants and establishment of new plants. We provide expert consulting through- out the entire process – from business plan and authority approvals to design and tender documents. We supervise the construction phase and during commissioning.
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By Finn Bruus, team leader, VEKS and Per Alex Sørensen PlanEnergi
The purpose of the project is fourfold: 1. To develop and demonstrate a PTES that can be operated in a more flexible and advanced way than has been seen to date. Thus, allowing charge and discharge of energy at a daily and weekly basis allowing flexible electricity production from CHP plants and peak shaving in large DH systems. 2. To develop and demonstrate new innovative technical solutions that can solve some of the necessary challenges needed to bring the PTES technology an important step further towards fully commercial scale used as accumulation tank in large DH systems. 3. To demonstrate, that the PTES can replace a similar steel tank and be implemented for less than 1/3 of the costs for a steel tank. The price for the PTES is expected to be 300 DKK/m3 (40 €/m3) compared with app. 1,000 DKK/m3 (133 €/m3) for a steel tank with the same capacity. In addition, costs for connections to the district heating network and pumps must be added for both the PTES and the steel tank. 4. To develop an optimization system for a PTES in a large DH system with a large number of stakeholders (heat producers and consumers). Implementation of the demonstration project will open a new huge market for PTES as a viable tool for DH systems to be effective integrators of fluctuating renewables. It will be demonstrated that the temperature in the upper part of the storage can be constantly fixed at 90°C making them able to replace the more expensive steel tanks. The objective is to make this possible by change of liners, insulation materials and design. Also, it will be demonstrated how advanced operation creates synergy between heat and electricity markets. A comprehensive monitoring program is part of the project. The construction work started June 2019 and the PTES will go into operation in autumn 2021. The construction starts with connections to DH networks, buildings for pumps and heat exchangers and after that the excavation work for the PTES will start.
This article gives an introduction to the “FLEX_TES” 70,000 m3 pit heat thermal storage (PTES) project, where the PTES will be demonstrated in a new function as accumulation tank in a district heating (DH) system with combined heat and power (CHP) from biomass and incineration. The energy content of the PTES will be 3,300 MWh. The use of the PTES means that energy production will increase on CHP and incineration plants, and there will be an optimization towards the electricity price. The electricity price varies, with the variation in wind and solar-based electricity production, but also with the hydro- power production in the countries around DK. In hours with high renewable electricity production, electricity prices are low, and the PTES must cause electricity and heat production to be transferred to plants with relatively low electricity production and vice versa. Furthermore, heat peak load production will be replaced by discharge from PTES. In the future, heat production will be transferred to electricity consuming technologies, such as large electricpowered heat pumps for DH, in hours where the electricity price are relatively low.
The PTES will be owned 50 % by transmission company VEKS and 50% by Høje Taastrup District Heating Company.
The project is supported by the Danish research and development program EUDP.
THE PURPOSE OF THE PROJECT The PTES will be demonstrated in Høje Taastrup DH Company’s distribution system but connected to the large VEKS´ transmission system (Fig 1) as part of the integrated DH system in Greater Copenhagen. This makes it possible for all the CHP plants in the transmission systems of VEKS and CTR to interact with the storage.
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TECHNOLOGY: STATE-OF-THE-ART Heat storages can be constructed in different ways – tanks, pit, borehole and aquifers as shown in fig 1.
No. of storage cycles
87 / 12 O C
89 / 12 O C
T-max. / T-min.
Heat capacity with T-max./T-min. 5,200 MWh
Fig.3: Dronninglund – PTES energy flow 2016 and 2014-20
INNOVATION IN THE FLEX_TES PROJECT The FLEX_TES project will demonstrate how the PTES, which was originally developed for longterm solar thermal storages, can be utilized to add flexibility to a large DH system with many different producers connected to the DH system. The PTES will be established in Høje Taastrup – a municipality in the western part of Greater Copenhagen - and integrated with the local DH distribution company Høje Taastrup DH Company as well as with the VEKS heat transmission system. The business case study for the establishment of the PTES has shown that the benefit of the PTES will be significantly higher if the operation of the PTES is integrated in the daily optimization of the large interconnected DH system in Copenhagen. The business case has shown that in order to obtain the highest benefit for the system the PTES will need to be operated to store/discharge energy on a weekly and daily basis. As part of the preparation of the project the operation of the PTES has been optimized using the software model Balmorel, which provides an economic optimization of the electricity and DH market. The model optimization shows that the PTES should be charged and discharged 25 times each year in order to have the highest benefit (fig. 4).
PTES has during the last 30 years been developed in Denmark as longterm storages for solar DH. The Technology Readiness Level (TRL) is 8 for PTES combined with solar thermal plants, but still there are problems to be solved. These are: • Lifetime for the PE-insulation in the floating lid. • Water ponds on top of the lid. • Oxygen in the storage water causing risk for corrosion in connected steel pipes.
The FLEX_TES project will bring PTES used as accumulation tanks from TRL 6/7 to TRL 8.
Full-scale PTES has been implemented in connection to: • Marstal DH Company in 2011-12 (75,000 m3 water) • Dronninglund DH Company in 2013-14 (60,000 m3 water) • Gram DH Company in 2014-15 (122,000 m3 water) • Vojens DH Company 2014-15 (220,000 m3 water) • Toftlund DH Company 2016-17 (70,000 m3 water). The results of the monitoring program in Dronninglund gives the energy balances for the three years 2014-2016 as shown in fig 2 and fig. 3:
Fig. 4: Modelled energy content in the storage during the year in Høje Taastrup with advanced oper-ating strategy.
This operating pattern for the storage is technically possible but it involves different challenges and needs to be developed and demonstrated. The PTES will work as an accumulation tank and will be charged and discharged several times during a year. That will change the water temperatures from being 85-90°C in a couple of months to constantly 90°C in the top of the storage. The system benefit of the PTES is via BALMOREL analyzed to be 6-6.5 mill. DKK/year (0.8 million €/year) using 2025 as an average reference year.
Fig.2: Dronninglund - PTES energy flow 2014 – 2016 (Source Solites)
All PTES’s in Denmark are constructed with soil balance and floating lid. The liner material for water tightening is a welded HDPE-liner, and the lid construction is either with PE- foam plates as insulation (Marstal and Dronninglund) or with expanded clay (Gram, Vojens and Toftlund).
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DEVELOPMENT OF AN OPTIMIZATION SYSTEM The recommendations of the Strategic Energy planning project Heat Plan III for Greater Copenhagen (2014), as well as the recent recommendations from the Danish Energy Commission’s report, highlight the potential ability of DH systems to be more flexible and become efficient integrators of fluctuating renewables (wind and PV). The recommendation for the Copenhagen area alone was to build heat storages in the magnitude of up to 10 times the storage capacity of the actual PTES in Høje Taastrup. A significant challenge for realizing such investments is to convince the investors that the storage will be operated in such a way that potential benefits can be attained in the real world. Currently, the operation of the Copenhagen DH system is operated by the central dispatch unit, Varmelast, which every day makes hourly based least cost plans for the operation of the production units and heat storages in the system. The plans are based on input from the different producers as well as forecasts for the heat demand and constraints in the heat transmission system. The optimization horizon of Varmelast is two days and it therefore does not take into account the value of the use of a storage beyond this time horizon. Therefore, it is necessary to develop an optimization system that can incorporate a longer planning horizon, for example, a week, and a different approach to optimization of the operation of a heat storage. The benefits of the PTES will be distributed between stakeholders. As the PTES will be integrated in the district heating system it will have an influence on all heat producers owned and operated by different companies (CHP, incineration plants, heat only boilers, geothermal plants and heat pumps.
The two main benefits of the PTES are: • that it can improve the flexibility of the DH system thus enabling 1) a better optimization of the production units in the electricity market, and 2) an increase of the heat production on cheaper units (CHP plants, geothermal energy and heat pumps), • decrease the production on more expensive units (natural gas and oil fired peak load boilers). In addition to saving expensive fuels, the PTES also reduces CO2-emissions by substituting fossil fuels with biomass and other renewable sources. Since the lifetime of the liners depends on temperature and oxidation, this will be a challenge to face in the FLEX_TES project. One of the possible liner suppliers has recently tested a liner at SP (Swedish test institute), and the Danish Technological Institute has also tested a liner, but in at shorter test period. The conclusion is that it is necessary to use a double liner solution to secure more than 20 years lifetime at 90°C. Also, the lifetime of the PE insulation will be a challenge since the melting point of the material used in Dronninglund is between 95°C and 100°C, meaning that the material will not stand 90°C in 20 years. But the supplier of the insulation in Dronninglund, is developing a new type of PEinsulation with a melting point at 120°C.
These two major challenges will be met when defining the demand specifications in the quotation of liners and insulation.
Since the storage function is to have the role as accumulation tank, on aweekly basis, for the entireDH system inCopenhagen, the in and outlet capacity has to be as large as possible. The inlet capacity will be 30 MW and the outlet capacity will be 30 MW, limited by the existing pipe connection to VEKS and the heat consumption in Høje Taastrup.
Fig. 5: Pumping station for the PTES
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