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: r.deboer@ecn.nl; 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

References

1. Deckert M, Reil S, Jakuttis M, Binder S, Hornung A. Mobile und stationäre Latentwärmespeicher Technik,

Wirtschaftlichkeit und Marktreife, Proceedings 13. Symposion Energieinnovation Graz 2014

2. Mehling H. Cabeza L. Heat and cold storage with PCM, 2008, Springer

3. Hauer A, Gschwander , Kato Y, Martin V, Schossig P, Setterwall F, Transportation of Energy by Utilization

of Thermal Energy Storage Technology, IEA ECES 18 report, http://www.iea-

eces.org/files/annex18_final_rept_october_2010.pdf

4. Guo S, Zhao J, Wang W, Yan J, Jin G, Wang X, Techno-economic assessment of mobilized thermal energy

storage for distributed users: A case study in China, Applied energy 2016

5. Zalba B, Marin JM, Cabeza L, Mehling H. Review on thermal energy storage with phase change: materials,

heat transfer analysis and applications, Applied Thermal Engineering 23 (2003) 251–283

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