Steel Industry Energy Recovery with Storage
Micaela Diamant Saga Rebecka Herlenius
Bachelor of Science Thesis
KTH School of Industrial Engineering and Management Energy Technology EGI-2019
TRITA-ITM-EX 2019:324 SE-100 44 STOCKHOLM
Sammanfattning
Svenskt st˚al AB (SSAB) ¨ar ett globalt st˚alf¨oretag som str¨avar efter att vara helt fossilfria ˚ar 2045.
Idag frig¨or SSAB Borl¨ange ˚arligen 20 GWh av ¨overbliven v¨arme i form av ˚anga till atmosf¨aren.
˚Angan kan ist¨allet f¨orvaras med hj¨alp av termisk lagring, och sedan anv¨andas igen f¨or att minska det fossila br¨anslet som idag driver ˚angpannorna. Den h¨ar rapporten kommer unders¨oka om SSAB Borl¨anges gamla oljetank p˚a 1200 m3kan bli omplanerad till en termisk lagringsenhet f¨or att f¨orvara
˚angan som g˚ar till spillo.
Resultaten visar att tanken kan bli designad som ett dagligt hetvattenf¨orr˚ad med en tv˚a centimeter bred isolering av ”foam polyurethane” och att en full tank kan f¨orvara 107,2 MWh. Det kommer leda till ˚arliga besparingar av olja upp till 2,14 GWh vilket kommer spara f¨oretaget runt 800 000 kronor om ˚aret i oljekostnader.
En teoretisk analys visar att SSAB Borl¨anges f¨oreg˚aende oljetank kan bli designad som ett hetvat- tenlager och kommer vara vinstgivande b˚ade f¨or milj¨on och deras ekonomi.
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Abstract
Svenskt St˚al AB (SSAB) is a global steel company who aim to eliminate all of their CO2emissions by 2045. Today, SSAB Borl¨ange releases 20 GWh of waste heat in the form of steam into the atmosphere annually. This steam could instead be stored in a thermal storage unit, and then used again to reduce fossil fuel burning that is currently running the steam boilers. This report will investigate if SSAB Borl¨ange’s old oil tank of 1200 m3 can be redesigned into a thermal storage unit to store the steam that is being wasted.
Results show that the tank can be designed as a 95◦C hot water storage with a two cm thick foam polyurethane insulation, and a full tank will be able to hold 107,2 MWh. This will lead to annual oil savings of 2,14 GWh, which will save the company around 800 000 SEK per year in oil costs.
A theoretical analysis prove that the SSAB Borl¨ange previous oil tank can be designed as a hot water storage and be profitable both environmentally and economically.
Contents
1 Introduction 9
1.1 SSAB . . . 9
2 Objectives 9 2.1 Thermal Energy Storage . . . 11
2.2 Thermal Energy Storage types . . . 12
2.2.1 Sensible Thermal Energy Storage . . . 13
2.2.2 Latent Heat Storage . . . 14
2.2.3 Thermo-Chemical Storage . . . 14
3 Methodology 14 3.1 Data Analysis . . . 15
3.1.1 Selected Storage Type . . . 16
3.2 Storage Capacity Calculations . . . 16
3.2.1 Full tank capacity . . . 17
3.2.2 Losses . . . 17
3.3 Storage Conditions . . . 17
3.4 Cost Evaluation . . . 18
3.5 Sensitivity Analysis . . . 18
4 Results and Discussion 19 4.1 TES Design . . . 19
4.2 Costs and Savings . . . 19
4.3 Sensitivity Analysis Results . . . 20
5 Conclusions and Future Work 20
References 21
6 Appendix 22
5
List of Figures
1 SSAB Borl¨ange’s steel production process. . . 10
2 Basic view of how the tank looks. . . 11
3 Schematic picture of the methodology practised. . . 14
4 Blown-off steam 2017. . . 16
List of Tables
1 Storage technology comparison.[3] . . . 13
2 Economic viability of TES systems as a function of the number of storage cycles per year.[3] . . . 18
3 Total Oil Savings 2017. . . 19
4 Total Savings in a year. . . 19
5 Savings if oil price increases or decreases. . . 20
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Nomenclature
Sign Name Unit
T Temperature ◦C
V Volume m3
t Time s
W Watt J/s
cp Specific heat J/kgK
L Length m
D Diameter m
κ Thermal conductivity W/mK
τ Thickness m
h Hours hours
ρ Density kg/m3
Q Heat flow Wh
Abbreviations EU European Union TES Thermal Energy Storage CSP Concentrated Solar Power TCS Thermo-Chemical Storage PMC Phase Change Material R&D Research and Development UTES Underground Thermal Energy Storage
DHW Domestic Hot Water ATES Aquifier Thermal Energy Storage BTES Borehole Thermal Energy Storage CTES (Rock) Cavern Thermal Energy Storage
i.e In other words
1 Introduction
1.1 SSAB
SSAB, short for Svenskt St˚al Aktiebolag, is a 140 year old, now global, steel company from Sweden.
The company develops high-strengths steels and has a number of approximately 14300 employees in 50 different countries, and it’s net sales reached 75 billion swedish kronor in 2018. SSAB is a leading producer on the global market for Quenched & Tempered Steels (Q&T) and Advanced High- Strength Steels (AHSS). Also strip, plate and tube products along with construction solutions. The company’s vision is a stronger, lighter and more sustainable world. While steel industry still remains a significant source of CO2 emissions, SSAB are continuously working on sustainable operations.
They come in around 7% below EU average of CO2 emissions, but aim to replace their blast furnaces with electric arc ones to reduce this number even more. The goal is to reduce SSAB’s current emissions by 25% by 2025, and eliminate them entirely by 2045, meaning that their steel production will be fossil-free by then. To achieve this, SSAB has joined Hydrogen Breakthrough Ironmaking Technology (HYBRIT) with Vattenfall, one of Europe’s largest electricity producers, and LKAB, one of Europe’s largest iron ore producer. With this new technology in process, SSAB will be able to eliminate 7% of the CO2 emissions in Finland, and 10% in Sweden.[1]
2 Objectives
Today SSAB burns a large amount of both natural gas and oil when creating steel, which is creating CO2 emissions. As previously mentioned, one of SSAB’s main goals is to prevent this and become more climate friendly, meaning that they want to reduce their use of oil and natural gas.[1]
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Figure 1: SSAB Borl¨ange’s steel production process.
In SSAB Borl¨ange’s steel production process shown in Figure 1, 20 GWh of steam is annually released into the atmosphere at an average of 186◦C and 11,5 bar. This waste heat could instead be stored in a thermal energy storage unit and later reused. If the waste heat can be stored, and then reused in the steam boilers, the amount of natural gas and oil that otherwise fuel the steam boilers can be reduced.
The main objective with this project is to design a thermal storage unit out of a given tank for the steam that is currently being released into the ambient air.
Figure 2: Basic view of how the tank looks.
The given tank is a 1200 m3steel tank with insulation of an unknown material and width. Previously the tank has been used as an oil storage, but has been emptied and washed out. When the tank was in operation the oil was kept at a temperature of 65◦C, open to the surroundings, i.e held at an atmospheric pressure. No further information of the tank has been given.
2.1 Thermal Energy Storage
Thermal Energy Storage (TES) includes several different technologies, all of which are based on the concept that thermal energy can be stored and used on demand by heating or cooling a storage medium. This demand may vary during time; all energy storage systems are designed to make energy available at the user’s request and provide when production exceeds demand. This means that TES systems can balance energy demand and supply over time for power generation and for heating and cooling applications.[2] TES systems can be installed in the form of distributed devices or centralized plants, where distributed devices have a power capacity of a few to tens of kW, while centralized plants ranges from hundreds of kW to several MW. Distributed devices function as buffer storage systems to aquire solar heat for commercial and domestic buildings to provide hot water and heating. Centralized plants are designed for big industrial processes, renewable power plants like concentrated solar power (CSP), conventional power plants and combined heat and power plants to store waste heat in different forms. However, whether the TES system is centralized or distributed, it improves the energy efficiency of energy-intensive industrial processes
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and sectors such as glass, cement, iron and steel.[3] While increasing energy efficiency they can also reduce energy consumption, costs and CO2 emissions by increasing renewables in the energy mix. Studies confirm that thermal energy storages decrease costs and green house emissions while simultaneously increase fuel efficiency drastically. Research also finds that both short and long term storage options, such as large thermal storages are key components in the pursuit for 100 percent renewable energy systems. The utilization of waste heat is expected to increase as a result of rising fossil fuel prices, and TES technologies are expected to expand significantly in Europe and Asia.[4]
2.2 Thermal Energy Storage types
TES systems are divided into three groups; Sensible TES, Latent Heat Storage and Thermo- Chemical Storage (TCS). These groups are further divided into several types of technologies.
Sensible heat storage stores thermal energy by heating or cooling a solid or liquid storage medium such as water, sand, rocks or molten salts which are usually kept in highly insulated storage tanks.
In latent heat storage phase change materials (PCMs) are used, which offer a higher storage capacity. TCS utilizes chemical reactions such as sorption to store and release energy, and enables even higher storage capacities. Today, sensible heat storage is commercially used whilst PCM and TCS-based storage systems are mostly still progressing.[5]
Table 1: Storage technology comparison.[3]
Technology Status (%)
Market/R&D Barriers Main R&D
focus Sensible TES
Hot water tanks (buffers) 95/5 Super insulation
Large water tanks (seasonal) 25/75 System integration Material tank, stratification
UTES 25/75 High cost, low capacity System integration
High temp. solids 10/90 High cost, low capacity High temp. materials High temp. liquids 50/50 High cost, temp. <400◦C Materials
PCM
Cold storage (ice) 90/10 Low temp. Ice production
Cold storage (other) 75/25 High cost Materials
Passive cooling (buildings) 75/25 High cost, performance Materials High temp. PCM (waste heat) 0/100 High cost, stability Materials
TCS
Adsorption 5/95 High cost, complexity Materials,
reactor design
Absorption 5/95 High cost, complexity Materials,
reactor design Other chemical reactions 5/95 High cost, complexity Materials,
reactor design As shown in Table 1, TES technology barriers are mainly related to high costs and the main R&D focus is on suitable materials. The more complex systems like PCM and TCS require more R&D efforts to enhance reacting materials and improve knowledge of system integration as well as process parameters. Each TES application require a specific design to be applicable to specific requirements and boundary conditions. The technologies listed in Table 1 will be explained further in the report.
2.2.1 Sensible Thermal Energy Storage
In the energy production sector, Sensible TES has significant commercial availability. As previously mentioned, the storage medium can vary. There are five different technologies classified as Sensible TES; hot water tanks, large water tanks, underground TES (UTES), high temperature solids and high temperature liquids. Hot water storage systems has shown to be a cost-effective storage option.
By ensuring high thermal insulation and optimal water stratification in the water tank, its efficiency is further improved. This technology can be used as a buffer for example in case domestic hot water (DHW) supply exceeds demand, and are usually 500 liters to many m3 in size. Building heating systems combined with solar thermal installations for DHW called solar-combi-systems also use this hot water storage systems. Large hot water tanks have a volume ranging to thousands of cubic meters and have a charging temperature of 80-90◦C, but can be improved by heat pumps when discharging leading to temperatures around 10◦C. This technology is mostly used for seasonal storage of solar thermal heat in small district heating systems.[3]
UTES is further divided into three technologies; Aquifer Thermal Energy Storage (ATES), Borehole
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Thermal Energy Storage (BTES) and Rock Cavern Thermal Energy Storage (CTES). In the ATES process, water is extracted from a well. The water is either heated or cooled before inserted into the aquifier again. Hence, thermal energy transfer is accomplished by mass transfer through the underground layer. ATES systems are mainly used for heating and cooling seasonal storage and are large at scale. The most common ground coupled technology for buildings is BTES, where projects aim for seasonal solar heat storage during the summer to warm both commercial and resedential buildings in the winter. Heat exchangers are vertically placed underground to achieve thermal energy transfer from and to clay, sand and rock in the ground layers. In Sweden, BTES systems supply 15 percent of all heating. There are only a few CTES examples in the world today, one of them made in Oulu, Finland. This storage consists of two close by rock caverns with a volume of 190 000 m3, previously used as oil storage for Kemira factory. Today, the caverns are full of hot water and connected to a cogeneration plant. This CTES is used for seasonal storage for the waste heat produced by Kemira factory and simultaneously as a short term storage for Oulu energy works. CTES are still, despite having been demonstrated in full scale, too expensive to compete with other hot water storage systems. However, sensible heat storage in general has a limited storage capacity due to the specific heat of the storage medium. It also has low energy density and variable discharging temperature.[6]
2.2.2 Latent Heat Storage
Latent heat storage is based on the storage medium changing states such as a solid/liquid or a solid/solid process. Some storage mediums often used are ice, Na-acetate trihydrate, paraffin or erytritol. PCM’s can be used both for short and long term energy storage, from daily to seasonal, by using different materials and techniques. While sensible heat storage has a low energy density and a variable discharging temperature, the use of PCM’s in latent heat storage can overcome these issues. For example, compared to 25 kWh/m3energy density for sensible heat processes, processes that involves energy densities up to 100 kWh/m3. Although PCM’s equals high costs, latent heat storage can be worth pursuing if the costs can be reduced.[3]
2.2.3 Thermo-Chemical Storage
The third thermal energy storage called Thermo-Chemical Storage (TCS) possesses significant advantages such as low volume requirements due to high storage density, low charging temperature and almost no heat loss when compared to other thermal energy storages. Adsorption is a thermo- chemical reaction, meaning the adhesion of atoms, ions or molecules to the surface of another liquid
Figure 3: Schematic picture of the methodology practised.
Figure 2 displays the methodology steps clearly; the project started off with information searching followed by data analysis, storage capacity calculations, storage conditions were set, a cost evalu- ation and a sensitivity analysis was conducted. Later, results were analysed and discussed. The information searching is presented in Introduction and Objectives, while the rest of the steps are presented below.
3.1 Data Analysis
To decide on which storage type was best fitted to the demands, calculations were made, based on statistics given by SSAB. Numbers from the figure below have been normalized because of confidential reasons.
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Figure 4: Blown-off steam 2017.
The graph in Figure 4 show that the blown-off steam is significantly higher in the summer, and is barely released in the winter. One can also see that boiler steam production is continuous during the year, if not slightly lower during summer months.
3.1.1 Selected Storage Type
After comparing when there is steam demand to when there is blown-off steam i.e waste heat by analysing Figure 4, and based on facts concerning different storage types in Table 1, it was decided that a sensible TES in form of a hot water storage would be favourable. Hot water storage is a relatively low cost storage. It is also a well known and commercially used technology with no
3.2.1 Full tank capacity
The maximum capacity of the tank was calculated. Depending on properties of the hot water, temperature of the ambient air and the tank volume, a maximum amount of heat stored per hour was calculated with Equation 1.
Q = V ρcp∆T
t [7] (1)
This would be the ultimate situation, i.e without losses. The heat flow was calculated per hour so it could be compared to the steam production and blown-off steam from the given data.
3.2.2 Losses
Depending on the properties of the tank insulation, length parameters and storing time the heat loss varies. The optimal length and diameter of the tank regarding heat loss would be if they are equal to each other (L=D).[8] Since information of the tank measurements are missing, this was assumed, and the formula could be simplified.
dT
dt = 6κ
τ ρcpD(T water − T air)[8] (2)
As Equation 2 shows, the temperature will drop at a certain speed depending on the tank diameter, insulation and tank thickness, thermal conductivity of the insulation, properties for saturated water and temperature of the ambient air. It is very important to have an insulation with a low thermal conductivity. Depending on the temperature drop the capacity of the tank will decrease differently every hour.
3.3 Storage Conditions
The capacity of the storage depends mainly on characteristics of the liquid and temperature dif- ferences between inlet and outlet. To be able to find out how much oil could be reduced with a hot water storage, the total capacity including losses was determined by setting some boundaries concerning charging and discharging of the storage;
• The storage should charge when:
1. The tank is not full 2. Steam is being released
• The storage should discharge when:
1. The tank is not empty 2. There is energy demand
These conditions were applied to the data available and iterations were made in Excel. The it- erations determined how much energy the storage is able to store in total of a year, which led to how much oil can be reduced by implementing the storage in SSAB Borl¨anges production process.
When the total amount of oil saved in a year had been calculated it was divided by the energy amount of one litre oil to get how many litres of oil that could be saved.[9] Then depending on the oil price per litre the amount of money per year that could be saved was calculated.
There were of course other conditions to consider as well, but these makes the basic design and so they are the only one considered in this report.
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3.4 Cost Evaluation
To decide if the chosen storage would be auspicious, a cost evaluation was necessary. Cost esti- mates of TES systems depend heavily on storage materials, technical equipment for charging and discharging and operation needs including the number and frequency of the storage cycles.
Table 2: Economic viability of TES systems as a function of the number of storage cycles per year.[3]
Cycles per year 5 year energy savings (kWh)
5 year economic savings (e)
Investment costs (e/kWh)
Seasonal storage 1 500 25 0,25
Daily Storage 300 150 000 7500 75
Short-term storage
(3 cycles per day) 900 450 000 22 500 225
Buffer storage
(10 cycles per day) 3000 1 500 000 75 000 750
Simplified calculations based on a 100 kWh storage capacity TES system with a thermal energy price of 0,05e/kWh explains how much energy savings and economic savings are made in five years based on how many cycles a year the storage exerts and the evaluation is presented in Table 2. The calculation focuses on the price of thermal energy and determines the cost range for TES to be economically competitive based on today’s energy prices. PCM and TCS systems are generally more expensive than sensible heat storage, which depends on the size, application and thermal insulation efficiency of the storage tank. Thus, PCM and TCS systems are only economically viable for applications with a high number of cycles per year. The reasons why sensible heat storages are rather inexpensive is because they basically consist of a simple tank for the storage medium and the equipment to charge/discharge, in this case hot water. However, the storage medium tank requires effective thermal insulation, which is an important contributor to rising costs since highly effective insulation is expensive.[3]
3.5 Sensitivity Analysis
Finally, a sensitivity analysis was conducted to determine how affected the system would be if some factors were to change. The main sensitivity factor would be oil prices, and possibly insulation
4 Results and Discussion
4.1 TES Design
When the steam is being released into the ambient air, the idea is to lead it through insulated pipes to the tank where a mechanism spraying cold water on the steam will be placed. The cold water will cool down the steam to 95◦C hot water. This is preferred, instead of using a heat exchanger, since there will be no energy loss in this process. After cold water spraying, the tank will store the 95◦C hot water until there is energy demand. A full tank will have a capacity of approximately 107 MWh, and should charge and discharge according to the conditions listed in section 3.3. The hot water that is discharged will be transported back to the steam boilers and reused in the production process.
Table 3: Total Oil Savings 2017.
Maximum saved daily Maximum saved yearly
Oil [MWh] 49,31 2140
Every hour a maximum of 2,14 MWh can be discharged and sent back to the boilers, which results in 2,14 GWh of steam per year and therefore approximately two GWh of oil per year can be saved, as Table 3 shows.
While the tank is charging the temperature will drop from its 95◦C to a lower temperature. As men- tioned in section 3.2.2 the drop depends on colder ambient air, thermal conductivity and thickness of the insulation, tank diameter and properties of the stored water. Since it was not known what kind of insulation the tank already has, the calculations have been made with foam polyurethane assuming that is the insulation used today and where the properties in the equations comes from.
With an insulation thickness of two centimeters the temperature drop would be 0,83◦C/day giving a capacity loss of 0,046% per hour. This temperature drop may vary depending on the properties of the existing insulation, if it’s even necessary to change insulation or better to use the existing one. The computations can be found in Appendix A.
4.2 Costs and Savings
The first and largest costs will appear during installation. The installation costs include work force pay and redesign costs concerning cold water spraying, but the most expensive and critical part will be the insulation.[3] Since these will be one-time costs, they have not been subtracted from the total savings of a year. However, in this project it has been assumed that the existing insulation in the tank is appropriate for storing hot water. But if the insulation would be unsuitable for this storage, it is proposed that foam polyurethane would replace the current insulation because of its low thermal conductivity and fairly low price of 103 SEK per cubic metre.[10][11] Insulating the 1200m3 tank with a two centimeter thick foam layer would cost around 123 600 SEK.[11]
Table 4: Total Savings in a year.
Price [SEK/litre] Amount in a year [litres] Saved [SEK] Total savings [SEK]
Oil [MWh] 3,75 213 633 801 124 801 124
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Table 4 [9][12] displays the total economic savings in a year based on today’s oil price. Without the neglected one-time installation costs, there would have been a total amount of approximately 800 000 SEK saved in 2017 with a hot water storage. This number will differ depending on how much the storage is able to discharge.
4.3 Sensitivity Analysis Results
An oil price forecast 2019-2050 estimates that oil prices could almost double until 2050.[13] This will only increase in economic savings for SSAB and is therefore not a risk. However, to be certain that a hot water storage will be beneficial, an analysis comparing an increase and decrease of the oil price with 7% respectively was made.
Table 5: Savings if oil price increases or decreases.
Price [SEK/litre] Amount in a year [litres] Saved [SEK] Total savings [SEK] Increase/decrease [%]
Oil [MWh] 3,75 213 633 801 124 801 124 0
Oil [MWh] 4,01 213 633 857 202 857 202 7
Oil [MWh] 3,49 213 633 745 045 745 045 -7
Table 5 shows that even if oil prices were to decrease (which is highly unlikely in the long run) a hot water storage would still secure large economic savings.
5 Conclusions and Future Work
Taking into consideration that the tank will be in use many years and that the installation costs are far lower than what the storage can save in a few years, installing this hot water storage is a profitable investment, not only economically, but also environmentally. The hot water storage will save SSAB Borl¨ange approximately 2,14 GWh of oil a year, resulting in 0,8 million SEK annually depending on how much the tank is able to discharge that year.
When calculating the results, some estimations were made. Transport losses were not taken into consideration, though these are inevitable even with high insulation. Calculating these will require the exact planned position of the storage to find out transport distance and will result in a more precise cost evaluation.
Something worth pursuing is to investigate if the hot water storage would be able to charge more if pressurized. More information about the tank would be necessary since it is not currently known
References
[1] SSAB, 2019. Energy efficiency.
https://www.ssab.com/company/sustainability/sustainable-operations/energy-efficiency [2] European Comission; Directorate-General for Energy (2012). DG ENER Working Paper. The
future role and challenges of Energy Storage.
https://ec.europa.eu/energy/sites/ener/files/energy storage.pdf [3] International Renewable Energy Agency.
https://irena.org/documentdownloads/publications/irena-etsap%20tech%20brief%20e17%20 thermal%20energy%20storage.pdf
[4] B.V.Mathiesen, H.Lund, D.Connolly, H.Wenzel, P.A.Østergaard, B.M¨oller, S.Nielsen, I.Ridjan, P.Karnøe, K.Sperling, F.K.Hvelplund. (2015). Smart Energy Systems for coherent 100% renew- able energy and transport solutions. Applied Energy Volume 145, Pages 139-154.
https://www.sciencedirect.com/science/article/pii/S0306261915001117?via%3Dihub
[5] REN21 .(2018). Renewables 2018, Globas status report. A comprehensive annual overview of the state of renewable energy.
http://www.ren21.net/wp-content/uploads/2018/06/17-8652 GSR2018 FullReport web -1.pdf [6] Nordell. B, (2012). Underground Thermal Energy Storage (UTES).
http://large.stanford.edu/courses/2013/ph240/lim1/docs/UTES Nordell.pdf
[7] Cengel. Y, Ghajar. A (2014). Heat and Mass Transfer: Fundamentals and applications. Fifth edition
[8] Chen J. (2011). Physics of Solar Energy. Chapter 12, Energy Storage.
https://onlinelibrary-wiley-com.focus.lib.kth.se/doi/pdf/10.1002/9781118172841.ch12 [9] Swea Energi AB, 2019. Fuel oil.
http://www.sweaenergi.se/produkter/eldningsolja/
[10] Aerofoam Insulation Solutions, Hira Industries LLC, 2019.
http://www.aerofoam.ae/water-tank-insulation/
[11] RS Components AB, 2019. Black Polyethylene Foam.
https://se.rs-online.com/web/p/products/7336696/?grossPrice=Y&cm mmc=SE- PLA-DS3A- -google- -CSS SE SE Abrasives And Engineering Materials- -
Rubber Sheets%7CPolyethylene Rubber Sheets- -PRODUCT GROUPmatchtype=&pla- 393935874913&gclid=CjwKCAjwq-TmBRBdEiwAaO1en2kBXpTsXcIO0YH27O1Na4HZ iYcEQwJX XdaN4b7XNbdu0TkvXtBlhoCYqMQAvD BwEgclsrc=aw.ds
[12] Creamfile AB, 2019.
https://www.oljepris.nu
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[13] Amadeo. K, 2019. Oil Price Forecast 2019-2050. https://www.thebalance.com/oil-price- forecast-3306219
6 Appendix
close all, clear all, clc
%Kandidatexamensarbete VT19
%%
%temperature drop
%properties of water
cp = 4212; %specific heat J/kgK rho = 961.5; % density kg/m3 V = 1200; % volume m3
D = ((4*V)/pi)^(1/3); %diameter m
deltaT = (95-20); %temperature difference degrees celsius kappa = 0.02; %thermal conductivity W/mK
tau = 0.02; %insultion thickness m
tempdrop = ((6*kappa)./(tau.*rho.*cp*D)).*(deltaT) %temperature drop, degrees/second
dygn = tempdrop * 3600*24 %temperature drop during a day
%%
%oil savings
oilprice = 3.75; %SEK today
blown = 2136330 %blown off steam 2017 MWh
energyoil = 10 %1 litre of oil approximately contains 10kWh litre = blown/energyoil %how many litres per year is saved priceayear = litre * oilprice %SEK/year
foam = 103 %SEK/m3
totfoam = foam * V %SEK for the whole tank
pricetot = priceayear - totfoam %oil savings minus foam cost SEK
%%
%Sensitivity analysis
%What would happen if the oil price increased/decreased with 7%
oilprice1 = 1.07 * oilprice priceayear1 = litre * oilprice1 oilprice2 = 0.93 * oilprice priceayear2 = litre * oilprice2
%saved in %
oilprice3 = oilprice1/oilprice oilprice4 = oilprice2/oilprice
