ROBUST OPTIMIZATIONAND DYNAMIC SIMULATION OF A

SMALL SCALE POWER-TO-AMMONIA PLANT

24/08/17 NEC Researchers days

Robert Weiss,Jouni Savolainen, Teemu Sihvonen,

VTT Technical Research Centre of Finland Ltd., Finland

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Contents

Introduction

Nitrogen fertilizer use in Europe

Small scale Power-to-Ammonia concept

Results: Sizing and operation of a Power-to-Ammonia plant

Dynamic simulation: Virtual tests of plant dynamics

Robust optimization and market operations: Scheduling, profitability

and CO2-emissions reduction in wind power intensive West Denmark.

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Source: European Spatial Monitoring System, 2011

Source: Eurostat, 2016

Nitrogen fertiliser usagein Europe 2005

Installed wind capacity in Europe 2011

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Source: European Spatial Monitoring System, 2011

Source: Eurostat, 2016

Nitrogen fertiliser usagein Europe 2005

Installed wind capacity in Europe 2011

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Power to ammoniaSmall scale ammonia production makes it possible to produce green decentralized ammonia which can be further used as:• Nitrogen carrier (fertilizer)• Hydrogen carrier• Energy storage• Fuel

Feedstock:• Electricity from renewable sources (Wind turbines, PV) • Air (via N2/O2 separation)

Source: http://www.protonventures.com

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Wind-driven Small-scale Ammonia mill

Windpowercapacity

Full loadNominal Capacity

NH3

Wind power: - Intermittency- Forecasting errors: Uncertainty, depends on forecast horizon

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Wind-driven Small-scale Ammonia mill

Windpowercapacity

PEMElectrolyzer

PEM

Overload Capacity60% /30min

H2Buffer

Flexible Ammonia process

H2

Full load

Part load 30-100%

Nominal Capacity

NH3

Market Power

Wind power: - Intermittency- Forecasting errors: Uncertainty, depends on forecast horizon

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High-fidelty APROS simulator model for virtual test of process dynamics and control concepts

Apros is a versatile high fidelty first principles dynamic simulator, including

thermal hydraulics networks, automation & control, and specialized dynamic models for

Power-to-gas electrolysis and Haber-Bosch synthesisetc

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Virtual test of power-to-ammonia dynamics: Primary Frequency Control operation in West Denmark (DK1)In this example test we used an optimal 5-days hourly operation plan for the power-to-ammonia plant:- Available wind power (Day-ahead Forecast)- Wholesales spot power purchase and sales (Day-ahead hourly)- Primary Frequency Control capacity sold (Day-ahead 4-hour blocks)- Running schedule for power-to-ammonia plant units (Day-ahead hourly)

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Virtual test of power-to-ammonia dynamics: Primary Frequency Control operation in West Denmark (DK1)

Power consumption including executed frequency control

With the contract schedules and TSO system frequency data (0.1-1s resolution), we calculate the actual primary frequency control response of the PEM electrolyser units.This allows us to calculate the fast dynamic responses of all subsequent process units, and the plant power consumption.

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Virtual test of power-to-ammonia dynamics: Primary Frequency Control operation in West Denmark (DK1)The operation mode performed well in the virtual tests.- Despite fast fluctuating power input, we achieved stable and

good operating conditions (p,T) for NH3 synthesis reactor - Some process valve controls had to be updated, especially for

very large and fast transients.- Gas storages operation schedules: Daily intial and end-target

storage levels important, some revision on sizes/max pressures

Power consumption including executed frequency control

NH3 synthesis reactor

Similar test results for following wind power production.

H2 balance and storage pressure

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Integration of wind power forecasting errorhandling…robust optimization

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Integration of wind power forecasting errorhandling… validation with apros simulation

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Small scale ammonia plantOperation optimization – example casesCase 1: Plant inside the fence of a Wind Park

Subcase G50%: Restricted grid connection to 50% of Wind Park max capacityIntra-day trade balances WP forecast error except for the final hour-ahead WP forecastRobust optimization reserves optimal capacity to mitigate worst-case errors in final hour-ahead WP forecastAssumed automatic load following within execution hour

Case 2: Plant in DSO grid, hourly Net Settlement with Wind ParkSubcase PFC: Plant is also able to sell Primary Frequency Control on day-ahead basis.

Load following not allowed.Robust optimization reserves optimal day-ahead capacity to mitigate worst-case distortions for prolonged PFC response.

Case 3: P2NH3 plant buying only market power and Certificates of OriginSubcase PFC: like in case 2.

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Example market area – West Denmark DK1 in 2016

For our example, we used • wind power production data, • power spot price data and • primary regulation price data of West Denmark, DK1 price and control area (Energinet.dk 2016; NordPool 2016).

DK1 spot price varied between -54 to 105 EUR/MWh and had an average of 26.7 EUR/MWh.

Grid fees in the cases ranged between 7.6 to 48.6 EUR/MWh.

This area is well known for a high intensity of Wind Power, which during peak production times was up to 200% of the power consumption in the area during 2016. In 2015, 42% of the power used was wind power.

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Case1: Plant inside the fence of a Wind ParkRestricted grid connection to 50% of Wind Park max capacity

12.5 MW Wind parkHourly power production as in DK1= same timing as DK1 market wind power

Grid connection only 50% = 6.25 MWWithout storage, 12.5% of the produced wind energy would be stranded

Grid connection capacity

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Case1: Plant inside the fence of a Wind ParkRestricted grid connection to 50% of Wind Park max capacity

12.5 MW Wind parkHourly power production as in DK1= same timing as DK1 market wind power

Grid connection only 50% = 6.25 MWWithout storage, 12.5% of the produced wind energy would be stranded-> This was avoided!

4000 tNH3/year ammonia plant5 MWe electrolysis (nominal)- 4 parallel PEM electrolysers- 60% overload capacity5 hours intermediate H2 bufferHaber-Bosch flexibility 30-100%

Grid connection capacity

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Wind power utilization and CO2 emission reduction

High Wind power utilization was reached for case 1 ”Inside Fence of Wind park” and case 2 ”Net Settlement”.

For case 3 ”pure market purchase”, only slighly higher WP than yearly average of grid was reached.

PFC operation increased slightly market purchases, decreasing WP share.

Case 3 increased the CO2-emissions of NH3 production, since the non-WP share of grid market power purchases contain a high share of Fossil based power, especially coal fired power.

Wind power utilization includes here both• direct ”own” WP, and• indirect grid WP (hourly share of market purchases, via settlement

calculation from DK1 official timeseries)

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ProductionCostsStrongly dependent on operation case

Primary Frequency control:Good income potentialAssymmetric Bidding in DK1 area is beneficial for electrolysers!

Compare to global market price range of 250-700 EUR /tNH3

for conventional fossil NH3

during 2010-2016

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ProductionCostsStrongly dependent on operation case

Primary Frequency control:Good income potentialAssymmetric Bidding in DK1 area is beneficial for electrolysers!

Some additional income potential from O2 sales (estimate 50-70 EUR/tNH3)

CAPEX share still very large

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Ammonia total production cost:Impact of CAPEX and Wind Power cost

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Summary and conclusionsSmall Scale Power to Ammonia example was shown for Danish wind power and market (DK1) conditions.

Operational planning needed to find economical case and CO2-reduction potential.”Net settlement with wind power” or ”Inside fence of Wind park” operation seems to be suitable in Denmark, while a pure market-based operation has clear drawbacks.

Process dynamics provides needed flexibility to meet intermittency of wind power. PEM Electrolyzer’s capacity to temporarily overload is beneficial.

Participation to electrical grid ancillary services (Primary Frequency control) is essential. DK1 assymetric bidding is beneficial for PtX.

Robust optimization was needed in the operational planning to include the effects of uncertainty for Primary Frequency control and mitigation of Wind Power forecast errors.

Competitive or at least acceptable NH3-prices seem to be reachable within near future.