Model predictive control as a way to maximize power production in Pump-as-Turbines

Using pump as turbines coupled with control valves can produce power and achieve pressure regulation at the same time. Pumps operating in the reverse mode can be used as an alternative to other hydro turbines due to its low payback time, low cost and low maintenance. Dŵr Uisce aims to install PATs in water networks using control valves in a configuration called the hydraulic regulation (HR). The figure 1. below shows the HR configuration in a graphical representation.

Figure 1 PAT in HR scheme

In HR scheme, there is a control valve used rather than a pressure reducing valve in which the pressure setting is constant rather than changing which is the case in a real network with flow variations throughout the day. The main advantage of using a control valve over a pressure reducing valve, better pressure regulation can be achieved due to fast closing and opening times. There are many types of control valves in the market for e.g., Ball, Globe, Butterfly, etc. The figure 2. below shows a better understanding of the types and relationship of flow with OD.

Figure 2 Types and relationship with flow and OD of different types of valves

For this work, globe valve is selected due to its linear relationship with flow rate and opening degree rather than compared with other types for e.g.: Butterfly valves have a non-linear relationship with flow and opening degree.

After selecting the best type of valve for the network and using the characteristics to model it, the next step is to model the PAT. Using a method developed by a fellow contributor to the Dŵr Uisce project, PAT model can be used combining with the valve model to use Model Predictive Control to maximize the power output based on the optimal flow and changing the Opening degree of the valve to accommodate it. Model predictive control is an advance control strategy used to control a process while satisfying a set of constraints. The main advantage of MPC is, it optimizes the current timeslot based on the past values, while keeping the future timeslots in account. This technique can be used to maximize the power output from the PAT based on the optimal flow which can be calculated and changing the opening degree of the valves accordingly to achieve pressure regulation.

Free green seminar on community energy

There is a 1-day seminar to explain the work carried out in the area to promote and support community energy. The event is primarily sponsored by two professional Engineering Institutions - IMechE and the IET. A number of speakers are being invited to what promises to be a very interesting and informative day talking about local community energy initiatives issues in North Wales. The audience will consist of practitioners and the general public. The seminar topics include micro-hydropower, solar energy, energy-saving initiatives and Electric vehicle.

Dr Daniele Novara (Trinity College Dublin) and Dr Prysor Williams (Bangor University) are representing the team to give a speech on micro-hydropower using Pump as Turbines and green initiatives from Dŵr Uisce Project.

The event will take place on 19 March and the venue will be the MSParc business park on Anglesey. Refreshments will be provided including a light lunch. If you are interested in knowing more about the Dŵr Uisce project, you may find the event registration link below.

https://nearyou.imeche.org/eventdetail?id=17561

Sustainable development across universities, businesses and communities

In February, Annum and Aisha attended the Office of Future Generations Commissioner for Wales event at Menai Science Park (M-Sparc) in Anglesey which was aimed at promoting the Well-Being of Future Generations (Wales) Act 2015 which was developed to improve the social, economic, environmental, and cultural well-being of Wales through sustainable development. Under this Act 44 public bodies are legally obligated to make changes to their current practices to become more sustainable for both current and future generations. The event was attended by students, businesses and prominent members of local community who were interested in learning more about the Act. This event was a great opportunity for the members of Dŵr Uisce team to learn how other organization and businesses view sustainability and how they may be able to implement some aspects of the Act into their businesses to make it more sustainable.

Annum and Aisha also attended a “Low Carbon, Happy Homes” event hosted by Menter Môn. Menter Mon is a not for profit that works with businesses, communities, and individuals to provide solutions to challenges in rural Wales. Low Carbon, Happy Homes is a project that aims to create awareness on the energy use and renewable alternatives to communities in Anglesey. Several small-scale energy savings projects have been introduced under this project which includes water and energy efficiency, electric bicycles, flow gas consortium of 27 houses that lead to cost-saving per litre of fuel and workshops to create awareness in communities on how they can be more energy efficient in LLanddona and LLanfealog communities. Presentations were also given by Renew Wales and Ogwen Partnership in which they discussed how they are helping communities tackle impacts of climate change in hopes to prevent rural poverty through environmental reforms. This event highlighted the importance of involving local communities to make Wales more sustainable. The participation of communities showed that they recognise the imminent threat of climate change and are willing to make changes to tackle it.

Brand New Dŵr Uisce Newsletter is out!

This time, we have revamped our newsletter to provide you with a brand new reading experience. Check our brand new newsletter here to learn what we have been doing.

Himanshu presented his research at Indian Control Conference in Hyderabad, India

Our postdoctoral researcher, Himanshu Nagpal, presented at the Sixth Indian Control Conference, which was held at Indian Institute of Technology, Hyderabad, India. The conference was devoted to advances in broad areas of control and system theory and their application in various areas. The ICC is held every year at a different academic institution in India. The organizer of the ICC is Control Society, a nonprofit society registered in India with the aim of fostering research and development activities in the broad domain of control and allied areas.

Schematic of wastewater assisted heat pump

Himanshu presented his work on improvement of energy efficiency in residential buildings using wastewater heat recovery and model predictive control.  His work demonstrated that the temporal mismatches between recovered heat availability and space heating consumption can be efficiently mitigated using thermal inertia of the building as a passive storage and applying model predictive control strategy to operate the heating system of the building.  The particular numerical case study presented in his paper demonstrated 26% reduction in total heating demand using wastewater heat recovery. The work presented is a small step forward in the direction of energy and water efficiency in domestic buildings.

Learning to use waste water heat recovery technology

By Isabel Schestak

Every human activity and every manufactured product carries an environmental footprint – that is no different for appliances or installations required to make water use more efficient. In this project, we look for example on the environmental footprint of a heat recovery system to recover heat from drain water.

A smart choice of materials and design can lower this footprint substantially and reduce emissions and resource use. By applying the Life Cycle Assessment (LCA) methodology, we determine the best way to design sustainable heat recovery systems. This is called eco-design.

We are aiming to make the eco-design guidelines for heat recovery systems available to all businesses who are interested in using this technology. This will be facilitated by a toolkit. Free to use and publically available, the toolkit will provide two things: firstly, advice for decision making such as: Is my facility a potential candidate for recovering heat from drain water? And secondly, giving advice from a design perspective: Which technology can be used and which materials are recommended?

The recommendations for business owners will be based on individual information that the users fill in themselves, such as data on the water use amount and pattern. Examples for businesses are restaurant and pub owners, breweries, distilleries and many more operating in and outside the food sector.

With the tool, business owners will have the chance to not only reduce the environmental impact of their activities but also save energy and costs for heating water.

Hydro-power Energy Recovery in Deep Mines

By Himanshu Nagpal

Extensive amount of water is used in deep underground mines for various purposes like mineral processing, drilling, dust suppression, washing equipment, ore transport in slurries and refrigeration (for deep mines). Australia’s mining industry water consumption in 2008-2009 was 858 M m3 where as Canada’s mining industry water consumption in 2009 was 675 M m3 . The Boliden Tara Mines site in Ireland is the Europe’s largest zinc mine, the world 9th largest. Underground mining in Tara mines requires around 4.5 million m3/yr of water.

Due to high elevation change, the pressure of used water becomes very high at deep levels of mine. Pressure reducing valves (PRVs) are used at regular intervals to maintain the allowed pressure in pipes which can range from 6 – 12 bar. The used water must be pumped out (dewatering of the mine) using pump stations at various locations. This dewatering of mine is an energy intensive process. For Tara mines, the pumping contributes 10% to its total energy consumption (185 GWh/yr). This potential energy of water going down the mines shaft can be recovered using pump as turbine (PATs) in place of PRVs.

Example Case Study –

• Kopanang Gold mine

• Free state, South Africa

• Single shaft mining at depth of 1350 m and 2240 m.

Figure 1 shows the simplified mine water reticulation network for this mine

Figure 1 Simplified mine water reticulation network

The average water consumption of the mine is around 19 Ml/day or 220 l/s. The available elevation head is 2286 m. The required pressure in pipes is 100 m or 10 bar.  The theoretical energy consumption of dewatering the mine is

Figure 2 shows the mine reticulation network with energy recovery devices. PATs are installed in place of PRVs and a turbine pump is installed on a single shaft.

Figure 2 Mine water reticulation network with energy recovery devices

The PAT design conditions for specific production level:

• Average water flow on the production level – 110 l/s

• Average Upstream pressure – 52 bar

• Average downstream pressure – 10.5 bar

• Efficiency – 77.2 % (based upon pump-turbine efficiency curve)

• 353 kW of power at peak flow of 110 l/s and efficiency 77.2%

• Investment cost – 230,000 Euros

• Payback period – 3.8 years

Requirements for TARA mines

 Our objective is to do a feasibility study to estimate the potential of hydropower recovery in Tara mines based upon measured data. The steps involved in the feasibility study are as follows

• Measurements of flow data though PRVs

• Measurements of pressure drop data across PRVs

• Based upon the measurement of flow and pressure data, define a design-criteria for PAT

• Cost estimation base upon designed system

• Estimate cost savings and payback period

Anticipating future water scarcity from climate change

By Richard Dallison

Water service providers in the UK face a vast array of challenges when it comes to planning their future operations and services; climate change impacts on the amount of water available for supply to consumers is key among these. In the future we are likely to see longer more accentuated seasons, this is particularly true for winter and summer, which are likely to become more cold and wet, and more hot and dry respectively.

This change in the timing and quantity of surface water available for abstraction by water companies for supply to consumers could lead to water scarcity problems unless steps are taken now to look at the scale and precise nature of these changes and to plan the necessary management to protect against these changes. For example, lower amounts of summer rainfall are likely to be compensated for by larger amounts of precipitation in the winter. However, if reservoirs already fill to capacity in the winter, and no new storage is developed, then this additional winter rainfall cannot be taken advantage of to help with the dryer summers. This is particularly true for Wales, as the vast majority (~97%) of water abstracted for supply to consumers is taken from surface water sources, in particular from upland impoundment reservoirs.

 By using hydrological models, such as the Soil and Water Assessment Tool (SWAT), we can look at how projected future climate changes will impact on surface waters. In particular in our work we have taken a worst case scenario approach in terms of future emissions, with representative concentration pathway 8.5 being considered – the IPCC scenario with the highest level of future greenhouse gas emissions. SWAT is a highly detailed hydrological model, which allows investigation of not only the changes in the quantity and timing of water supply, but also the quality of that water. To this end, we can investigate how pollutants such as nitrogen, phosphorous, and suspended sediments will alter under climate change. Alterations in water quality could impact heavily on water companies, as more polluted water may require more rigorous treatment at drinking water treatment plants. These increases in required treatment to maintain drinking water quality standards could have impacts on the operational efficiency of the plants, both financially and in terms of energy use. In certain cases, it may even be required to upgrade plants with new technologies and treatment methods in order to cope with such changes.

Warming trend in average autumn temperatures displayed five catchments in Wales. Linear trend line for the Dyfi catchment shown in red to exemplify the linear trend in all catchments

Furthermore, if we also look at how demand for water is influenced by weather conditions, we can see a strong positive correlation between total water use (domestic, agricultural and industrial) and average daily temperature. When it is considered that future summers are likely to become warmer and dryer, this relationship is likely to put increased pressure on a supply-demand balance that may already be water scarce due to reduced summer rainfall. We can already see the effect of the aforementioned prolonged seasons, with summer temperatures stretching further into the autumn over the past 30 years; the below figure shows the increase in annual autumn temperatures between 1982 and 2015 for the five catchments in Wales. This figure demonstrates the further the need for thorough water resource management planning in order to ensure the continued supply of clean drinking water into the future.

Festive wishes from Dŵr Uisce

Thank you for collaborating with the Dŵr Uisce cluster during 2019. Together, we have innovated! Looking forward to 2020, we will be running several workshops, events and initiatives in the New Year. Our next newsletter will be published in February. Merry Christmas!

Benchmarking energy and economic efficiency across water utilities

By Nathan Walker

Benchmarking is the practice of comparing processes via performance metrics against each other, in order to ascertain a best practice for that process for others to learn from. The process in question can almost be anything, from rollercoasters and snooker chalk (yes, really) to pumps and water companies. Due the nature of our project, water companies were the subject of benchmarking in this research. Despite the UK water sector being mature in benchmarking, we believed we could add extra value to the companies, as well as academia, by applying new methodologies to analyse the efficiency of their operations, along with factors that may influence those efficiencies.

Figure 1. A basic schematic of the operations that a water utility conducts.

Initially, the approach in benchmarking comprised of stand-alone indicators (e.g. volume of water produced). Then to encompass at least some fairer level of comparison, partial indicators became prominent such as volume of water produced/population served and spending/volume of water treated. In academia, benchmarking has largely branched in to techniques that are slightly more complex. We chose data envelopment analysis (DEA), a non-parametric frontier approach to analyse a sample of UK and Irish water and sewage companies, which has the advantage of integrating multiple input and output metrics, and giving a value for each company that is determined relative to others in the sample. Specifically, we utiltised a double-bootstrap version of DEA that allows statistical inferences and hypothesis testing, essentially meaning we could investigate how other indicators may influence the efficiency of a company’s core operation (inputting energy and money to produce clean drinking water and treat wastewater), whilst avoiding some statistical errors that occur with techniques that similar objectives.

Results from the research indicated that companies across the UK and Ireland could on average reduce their economic and energy inputs by 19% and 16%, whilst maintaining the same levels of water delivery and treatment outputs. Furthermore, we found that the method we used changed the rank of over 65% of the companies, compared to the standard DEA model, showing the importance of utilising the most appropriate approach design. Finally, research so far has highlighted external variables that influence efficiency. Population density and the percentage of water abstracted from surface water showed to have a significant positive impact on both economic and energy efficiency, whilst leakage and number of abstraction sources were concurrent in their significantly negative influence across both energy and economic performance. Moreover, average pumping head height and consumption per capita displayed a significant negative effect for energy, conversely the variable proportion of water passing through the largest 50% of treatment works was deemed to have a significant negative effect on economic efficiency. Recommendations from this area of the research so far include: reduction campaigns for consumers, leakage reduction, evaluating security of supply vs. efficiency for number of sources, assess the potential to reduce head heights within new and existing networks, and investigate the optimal size of treatment plant to utilise economies of scale.

Some of these results are quite rare, whilst some may seem more obvious, however giving evidence towards certain areas helps to inform decision-making and prioritisation. This is one of the key advantages that benchmarking can offer, along with identifying those who have best practice, the idea being that the benchmarking ultimately facilitates sharing of these best practices. To ensure benchmarking can facilitate companies to perform optimally, improvements in transparency and communication is still required, which in theory is one of the easier hurdles to leap since the water sector already collects and stores the crucial data.