Techno-economic analysis of the Sailing Heat concept R. de Boer (ECN) E. Klop (IEE) S.F. Smeding (ECN) H.A. Zondag (ECN) March 2017 ECN-M--17-009 Presented @ SusTEM Conference 2017
Techno-economic analysis of
the Sailing Heat concept
R. de Boer (ECN)
E. Klop (IEE)
S.F. Smeding (ECN)
H.A. Zondag (ECN)
March 2017
ECN-M--17-009
Presented @ SusTEM Conference 2017
Techno-economic analysis of the Sailing Heat concept
Robert de Boer1*, Egbert Klop2, Simon Smeding1, Herbert Zondag1
1 Energy Research Centre of the Netherlands, PO Box 1, 1755 ZG Petten, The Netherlands 2 Industrial Energy Experts, IEE, PO Box 140, 6710 BC Ede, The Netherlands
* Corresponding author. Email: [email protected]; Tel. +31 (0)88 575 4871
Abstract
Sailing Heat is a concept for transportation of industrial waste heat over waterways by means of push barges to a heat
consumer. This concept is studied for the Netherlands where transport by ship is attractive thanks to the many canals
and industries located near waterways. The sailing heat concept offers higher flexibility compared to fixed district
heating pipelines and can be more cost effective in comparison to road transport. The concept is based on storage and
distribution of heat at temperatures between 80 and 120°C and large-scale transport of more than 500 GJ per unit.
The study includes the development of a thermal storage concept that offers a high thermal storage density based on
Phase Change Materials (PCM) for heat storage. Potentially applicable PCM’s were selected based on literature study
and small scale thermal analysis experiments. MgCl2•6H2O was selected as PCM having the right combination of
melting temperature, storage capacity, stability and cost. The design of the PCM thermal storage container was
elaborated, using thermal modelling to obtain the distribution of heat exchange area in the container to deliver the
required thermal powers for charging and discharging. The economic analysis of the Sailing Heat concept includes the
estimation of capital cost and operational cost to transport the heat by boat over a distance of approx. 20 km between
industry and heat user. The revenues are based on the amount of heat sold at the end user at market prices. The
calculated payback period is just over 15 years, which is comparable to payback periods in conventional district heating.
An increase of gas prices will reduce the payback period. The sailing heat concept can give a reduction of CO2
emissions for heating by 90%, compared to gas fired heating, and offers a very flexible concept to re-use industrial
waste heat. Further development of the sailing heat concept requires upscaling and cost reduction of high temperature
PCM storage concepts as well as availability of cost-effective and stable PCM bulk materials. In addition, subsidy
schemes to stimulate renewable energy (heat) production can also help to demonstrate CO2 emission reduction solutions
such as the sailing heat concept.
Keywords: Waste heat recovery and reuse; thermal energy storage; heat transportation; techno-economic analysis
1 Introduction
The demand for thermal energy constitutes the largest share in the energy consumption of existing buildings in northern
European countries. Substantial thermal energy savings in these existing buildings requires major renovation of homes
or buildings, with associated high investments. To achieve the national sustainability goals, the recovery and reuse of
available waste heat can provide a cost-effective way to further reduce CO2-emissions.
The Netherlands is highly industrialised and has many processes that emit waste heat, which cannot be recovered and
reused on site. One reason for not using this residual heat is the large distance between heat supply and heat consumers
and the high investment cost in district heat infrastructure. The transport of heat with a ship offers a solution to this
problem. Industrial areas with waste heat are often located near waterways, because the supply of energy, feed stock,
and the ability to discharge waste heat to the water.
To arrive at economically attractive solutions for transportation of heat, the thermal energy needs to be stored in a
compact manner. Transportation of thermal energy in a storage medium with a high storage density can be achieved by
the use of phase change materials (PCM)[1]. These materials can store the thermal energy in the phase change between
solid to liquid, known as latent heat storage [2]. This is a well-known principle for the storage of cold thermal energy by
using the phase change from solid ice to liquid water. A PCM that has its transition temperature in the range between
80-120°C is required for heat transportation, in order to match with the heat demand in the buildings and the waste heat
supply of industry.
The objective of this study is to assess the technical and economic feasibility of heat transport by ship with PCM
thermal storage for application in the Dutch energy market. For that reason a screening and selection of applicable
PCM’s is done, a preliminary arrangement is made of thermal storage units in the transportation concept on a push-
barge as well as a thermal design of the storage unit. The investment and operational costs of the sailing heat concept
are calculated and used for economic feasibility and comparisons with current heat prices.
2 The sailing heat concept
The concept of heat transportation from industrial waste heat location to final consumers over waterways is
schematically depicted in the scheme below. In this scheme it is considered that a single party is responsible for the
collection of industrial waste heat (1), takes care of storing and transportation between supply and demand (2) and
delivers the heat (3) to site of the heat consumer. The concept is as close as possible to real world situations where it
comes to collecting industrial waste heat and delivering heat to a network of consumers. Comparable studies were done
for transportation by trucks in Japan, Sweden, Germany and China [3,4]. For the analysis of the business case of the
sailing heat the current market prices for delivery of heat to consumers and for collecting heat at the industry were
considered.
The temperature for heat delivery to a district heat network should be sufficiently high to allow the heating of buildings
and for hot tap water. Normal supply temperature in the existing heat distribution networks is in the range of 80-90°C.
In order to have heat of sufficient temperature at the point of delivery the minimum waste heat temperature should be
well above 90°C. Waste heat with a temperature in the range of 150-130°C is considered in this analysis.
Figure 1: Schematic representation of the sailing heat concept, focused on the business case analysis.
2.1 Thermal energy storage and transport by a push barge
To assess the feasibility of the heat transport concept, a program of requirements for the intended applications was
drafted. It contains the technical requirements for thermal storage capacity, average charge and discharge powers and
temperature levels, the heat exchange concept to be used with the PCM, dimensions of the push barge, and transport
capacity. It also contains the requirements to be compliant with the applicable rules and regulations for safe
transportation over waterways.
In the elaboration of the system concept it is assumed that the heat is transported by two push barges, which are
equipped with 28 PCM tanks, as shown in figure 2. A push boat is used to push the barges from heat source to heat
supplier and back. A cycle of bringing a thermally charged barge to the heat consumer and returning the discharged
barge to the heat supplier is considered as reference case. In this situation it is of importance that the timing of charging,
discharging and transportation are such that the demands for the heat supply system can be met. In the optimal situation,
the charging time is so much shorter than the discharging time, that this compensates for the time to transport the
containers between supply and demand. In this situation the heat supply can be continuous.
Figure 2: top view of a push barge equipped with 28 PCM thermal storage units.
2.2 Thermal design of a PCM thermal storage unit
A Matlab model was made to determine a thermal design of the basic PCM thermal storage unit and to simulate the
charge and discharge characteristics of a single unit. The dimensions of the tank in the simulation are 4.2 x 4.2 x 3.2
meter (W x L x H), of which 28 units can be placed in the push barge. The unit is filled with PCM and nylon tubes are
considered to be used as internal heat exchanger in the container. The tubes transfer the heat from PCM to the heat
transfer fluid (water) and vice versa. The tubes of 16 mm internal diameter are arranged in a triangular pitch at a
distance of 50 mm. Total tube length is 25000 m, and 1250 m2 of heat exchange surface between tubes and PCM. The
tubes are arranged in 16 vertical passes, giving a single tube length of 50 m and 500 tubes in parallel. The main
parameters for the calculation and the resulting performance figures of a storage unit are given in table 1. The charge
and discharge characteristics of a single PCM thermal storage unit are shown in figure 3. The results indicate that the
batch character of the storage unit comes along with large changes in the thermal powers during the charging and
discharging phases. After initial high heat transfer rates, the increase in heat transfer distances through the low
conductive PCM, makes the heat transfer rate to slow down. It is also clear the charging process has lower average
thermal powers and therefor takes almost 4 times longer than the discharge process. The reason for this is that in the
simulation the temperature difference between the phase change and the heat transfer fluid during the charging process
is just 10°C, whereas in discharging it is 40°C.
Table 1: Overview of main characteristics of the thermal storage unit.
Description Unit Value
Phase change material - MgCl2·6H2O
Phase change temperature [°C] 117
Charge temperature [°C] 127
Discharge temperature [°C] 77
Average charging power [kWth] 400
Average discharing power [kWth] 1600
Max. charging power [kWth] 3000
Max. discharging power [kWth] 3400
Flow [m3/hour] 220
Average ΔT charging [°C] 1.6
Average ΔT discharging [°C] 6.3
Velocity water in tubes [m/sec] 1.08
Time full charging [hour] 16
Time full discharging [hour] 4
Thermal storage capacity [GJ] 23
Figure 4: Results of thermal power calculation during charge and discharge of a thermal storage unit.
2.3 Screening and selection of PCM
The list of potential materials that can be applied as PCM for compact heat storage is long [3]. In order to identify those
materials that are most suitable for the target applications, selection criteria are defined. The following set of criteria is
applied to obtain a ranking and a pre-selection of suitable PCM’s for the sailing heat concept.
Phase change temperature
The temperature of the phase change has to be between 80°C and 120°C.
Energy storage density in kJ/kg and in kJ/m3
For this criterion holds: the higher the energy storage density, the better it is. Both storage densities, gravimetric and
volumetric are included in the evaluation, because in the sailing heat concept the total weight is important for the
maximum charge of the ship, the total volume is important for the cost of the containers and heat exchangers of the
storage concept. The storage densities are calculated based on the latent heat as well as on the sensible heat from 80°C
to 120°C.
Cost of PCM
The cost of PCM is calculated based on €/MJ price. This price per MJ makes it possible that materials with a high
storage density also may have higher cost per kg. Price levels of bulk chemicals in amounts of 1 ton are considered. As
rule of thumb it is taken that feasible PCM’s should be below 5 €/MJ.
Safety-health-environmental (SHE) aspects
PCM’s should be safe to handle, with acceptable health and environmental impact. This is evaluated based on the
NFPA-704 designation, or safety diamond, for the respective PCM. Materials with scores on health 2, fire 2, and
reactivity 1 are only taken into consideration in the screening.
In the selection and ranking of the PCM’s a scoring was used on the various criteria according to table 1. A maximum
of 90 points could be obtained when a material had the best score on each individual criterion. A literature and internet
search was done to collect information on the properties of the potential PCM’s that fitted in the T-range of 80-120°C.
charge
discharge
Thirty materials were identified as applicable PCM’s. Besides the materials shown in the figure above, another 40
materials and mixtures were found, designated as materials in R&D phase. These materials are mainly based on
mixtures of organic acids, mixtures of nitrate salts and some high melting paraffin’s.
With the scores applied to the long list of PCM’s a ranking of materials arises as is shown in figure 3. This figure shows
the scores of the PCM’s, including those that were eliminated due to the knock-out criteria on cost or on Safety Health
Environment issues.
Of the 30 materials, 20 were knocked out due to high cost or high SHE scores. Salt hydrates were the main group of
materials with good scores for application as PCM in sailing heat. Also HDPE (high density polyethylene) had a good
ranking.
Small scale thermal analysis experiments (DSC, differential scanning calorimetry)on samples of ~ 20 mg were
conducted on the selected materials as a first experimental assessment of their practical use as heat storage material and
to support the selection process. An important aspect of the analysis was the stability of the materials during three
repetitive heating and cooling cycles. Stable melting and solidification behaviour was observed for MgCl2•6H2O,
MgNO3•6H2O and for HDPE. The salts did show subcooling of about 20°C in the re-crystallization phase. This means
that the heat release of the phase change occurs at a lower temperature than the heat uptake. This effect is well known
for salt-hydrate based PCM’s and can be reduced through additives in the PCM that enhance the onset of crystallization.
Table 2: Criteria and scores for selection of PCM for the sailing heat concept.
Criterion Unit Optimum
value
Range Score Knock-out criterion
Melting temperature C 100C 20°C 0 < 80°C or > 120°C
Energy storage density
(latent + sensible )
from 80-120°C
kJ/kg (2/3)
kJ/m3 (1/3)
Highest
found
150 kJ/kg up
to highest
found
30
15
< 150 kJ/kg
Bulk price €/MJ 0 Up to 5 25 > 5 €/MJ
Safety-Health-
Environment
Health
Fire
Reactivity
- Lowest
found
Up to
2
2
1
10
5
5
> 2
> 2
> 1
Total score 90
Figure 2: Scores and ranking of PCM in the preselection stage.
The other materials all showed a decline in the heat of melting during the second and third cycle. For the sulphate (SO4)
based salts, for erythritol and for oxalic acid the solidification and heat release upon cooling was very poor, which
resulted in a decline in the heat of melting when heated for a second and third time. This is an indication that the
reversibility of the phase change from solid to liquid and back to solid is limited. This makes a material not suitable for
the intended application.
Based on the results of the screening and the thermal analysis experiments MgCl2·6H2O was selected as the preferred
PCM for further study of the techno-economic feasibility of the sailing heat concept. 3 Economic analysis
The economic feasibility is based on the business case model as shown in figure 1. In this business case the investment
costs, operational costs and revenues from selling heat are allocated to a single party. The revenues consists of selling
the heat, for example to the operator of a district heating network. The price for the heat (€/GJ) equals the gas price in
this business case. Combining all three functions in one party is in fact an imaginary situation. In practical situations it
can be more separated. One party can be responsible for the recovery of the heat from the industrial process.
Another party can be responsible for the transport of heat, and a third party will distribute and sell the
heat to the consumers.
In the business case analysis two barges are considered to transport heat from supplier to consumer, with one pusher
ship. The characteristics of the push barge are shown in table 3. The heat demand is considered constant at 10 MWth
and equal to the heat source. The time to transport the barge, connect and disconnect the barge is assumed to be 4 hours.
This is based on a distance of 20 kilometres and velocity of 12 km/hour.
Table 3: Characteristics of the push barge.
Description Unit Value Remarks
Class barge [-] CEMT class Va
Type Europa IIA
Capacity 2,800 ton
PCM content [ton] 2,520 Based on density of PCM of 1.500 kg/m3 and
weight of PCM is 90% of total weight.
Energy content [GJ] 624 167 kJ/kg melting heat, + sensible heat at max
ΔT of 72 °C, 90% effective discharging factor.
Max. Charging
power
[kWth] 7,000
Max. Discharging
power
[kWth] 22,400
3.1 Energetic balance and revenues of heat delivered
With the charging time and transportation time to be the rate limiting step, a total number of 300 charge-discharge
cycles is achieved with the 2 barges. This gives 188000 GJ/year of heat delivered at the consumer, equivalent to the
consumption of 5.9 million m3 of natural gas.
To transport the thermal storage barges the ship needs a calculated amount of diesel of 6700 GJ/year and a comparable
amount is calculated for the primary energy needs for electricity (650000kWh) to run the pumps for the heat transfer
fluids.
The primary energy ratio of energy consumed over thermal energy delivered is 7%. The calculated carbon ratio, being
the ratio of CO2 emitted over CO2 emissions avoided, is 9%.
The revenues for selling the heat to the customers amounts to 1.19 M€ /year,
3.2 Investment cost
An overview of the investment costs for the heat transportation concept with two barges is given in table 4.
Table 4: Estimation of investment cost. Description Costs
Heat recovery at supplier € 427,000,-
Adjustments at heat consumer € 510,000,-
PCM-containers (2x28) € 4,840,000,-
Push barges (2x) € 800,000,-
Tax benefits -/- € 479,000,-
Total investment € 6,098,000,-
3.3 Operational cost
The annual operating cost for the sailing heat concept are calculated based on the following assumptions Staff costs: the
costs for the crew (2 persons) of the pusher is based on a tariff of 60 €/hour. This is the average tariff in the daytime,
night-time and during the weekends. The amount of hours required per transport is 4 hours, based on the distance, speed
and time to connect and disconnect the push barge. The amount of transport is 314 per year. One transport is bringing a
full barge to the consumer and return an empty barge to the supplier.
Fuel costs: these are the diesel costs for the pusher;
Various costs: insurance costs and berthing fees;
Maintenance costs: based on 2% of the total investment;
Electricity costs: electricity is used to pump water through the tanks. A high flow and a high pressure drop leads to high
electricity consumption. The electricity consumption is 650.000 kWh/year.
The waste heat at the industrial site is considered to be obtained free of charge.
Table 5: overview of annual operational costs.
Description Costs
Staff € 292,000
Fuel € 133,000
Various € 41,600
Maintenance €132,000
Electricity € 37,600
Total costs € 636,200
3.4 Financial result
This paragraph shows the financial results: payback period, NPV and IRR.
In the calculations, the following assumptions are made.
· WACC: 7%.,( weighted average cost of capital)
· Inflation: 2%.
· Indexation gas price: 1,5% per year.
· Indexation electricity price: 0% per year.
The table below shows the payback period, Nett present value after fifteen years and IRR, based on
the costs and revenues, which are shown in the previous paragraph.
Table 6: Results of financial analysis.
Description Value
Simple Payback time 11.1 years
Nett present value (15 years) NPV) -/- € 706000
Internal Rate of Return (IRR) 5%
4 Discussion and conclusion
In this study the technical and economic feasibility for recovery and reuse of industrial waste heat by means of the
sailing heat concept in the Dutch situation was assessed.
Despite the clear advantages in terms of primary energy saving of more than 90% as well as CO2 emission reductions of
90%, the economic analysis of the considered business case shows that with the current energy prices for fossil based
heating, the profitability of the sailing heat concept is too low to be attractive for potential investors. It would need a
subsidy scheme to stimulate the re-use of ‘carbon free’ waste heat as replacement for fossil heat sources, or a CO2
pricing mechanism on fossil based heating in the order of 50 €/ton CO2.
On the technical level several challenges were identified that need attention in the further development and future
implementation of this energy saving concept. The selection and development of PCM’s that have a proven stable
performance at the relevant scale (several m3) and for the required lifetime shows that only very few materials remain as
potentially suitable for the sailing heat application. Although the use of PCM as thermal storage materials is well
established in cold applications and in the thermal comfort temperature range for buildings, their use for high
temperature applications above 80°C is still limited to lab scale prototypes.
As shown in the business case, the temperature of the phase transition should be such that a good match is obtained with
the requirements for charging and discharging. The charging time was by far the slowest step, reducing the total amount
of energy transported. In ideal conditions a process designer would choose from a range of PCM’s that have transition
temperatures matching very close to the optimal temperature. In practice we are still far from this situation when it
comes to PCM’s in the temperature range 80-120°C considered here.
Another cost adding aspect of PCM’s is their low thermal conductivity. This results either in slow charging and
discharging processes, or in installing large heat transfer surface area, adding to the total investment cost. Improving the
thermal conductivity of a PCM can reduce system costs, give faster charging-discharging cycles, which increase the
energy saving potential and improves the annual revenues.
Acknowledgement
The development of sailing heat is supported by the TKI-Energo program of the Dutch government
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