H2 Compressor - Hyjack : Hydrogen Online
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About Tech
Hydrogen Compression
The hydrogen compressor calculator aims to:
1 - Develop a relationship between the inlet and outlet pressure, power and nominal flow rate.
2 – Generate a first level estimation of the compressor cost.
Hyjack offers a calculator for the three major mechanical compressors used for hydrogen gas: centrifugal, reciprocating (piston) and diaphragm.
The centrifugal compressor is usually recommended for relatively moderate discharge pressures and high flow rates compared to reciprocating compressors. Centrifugal compressors operate by the transfer of energy from a rotating impeller to the gas.
The reciprocating (piston) compressor is usually recommended for relatively high discharge pressures and moderate flow rates compared to centrifugal compressors.
The diaphragm compressor is a special type of the reciprocating compressor. In fact, the diaphragm compressor is used to handle toxic or flammable gases like hydrogen since no leakage is possible to the environment in this type of compressor. Diaphragm compression is unique in that a compression application that could require three to five stages in traditional types of compressors can be done in one to two stages in diaphragm compressors. Diaphragm compression can run 20-60% cooler on outlet temperatures than other types of compression technologies. This advantage enables downstream cost benefits including lower operating and maintenance costs.
The major difference between the reciprocating piston and diaphragm compressors is in how the gas is compressed. In a piston compressor, the piston is the primary gas displacing element. However and in a diaphragm compressor, compression is achieved by a thin metal, rubber or fabricated disk which is caused by the hydraulic system and operated by the motion of a reciprocating piston in a cylinder under the diaphragm.
The same iterative methodology is followed to determine the number of stages for the three types of compressors where the maximum discharge temperature is set to be 140 °C. At each stage, the work of the engine is calculated using the corresponding equation depending on whether a centrifugal or reciprocating/diaphragm compressor is chosen. Then, the power or flow rate is calculated. The discharge temperature and the temperature at each stage is calculated using the following formula assuming an isentropic behavior (adiabatic and reversible compression)
Centrifugal Compressor:
Where:
y is the isentropic coefficient Cp/Cv
Z1 and Z2 are the compressibility factors
R is the universal gas law constant
M is the molar mass
Q is the flow rate
q is the density
Isentropic Efficiency constant at 77%
Mechanical Efficiency constant at 79%
Electrical Efficiency constant at 95%
Leaks constant at 3%
Reciprocating Piston and Diaphragm Compressors:
Where:
Y is the isentropic coefficient Cp/Cv
R is the universal gas law constant
M is the molar mass
Q is the flow rate
q is the density
Mechanical Efficiency constant at 79%
Electrical Efficiency constant at 95%
Leaks constant at 3%
Isentropic Efficiency for diaphragm compressor constant at 85%
Isentropic efficiency for reciprocating compressor calculated from the following relation:
Where:
r is the compression ratio P discharge/P suction
It is also worth mentioning that an upper and lower bound are applied to the isentropic efficiency and are 85 and 60 % respectively.
Customisable parameter: the inlet temperature of the gas is set to 20°C in the standard model. However, the hydrogen flow or the power of the compressor can be recalculated with user given inlet temperature set in “customizable parameters” (in °C or °F).
About costing
The significant impact of th scale effect
The costing equations have been calibrated by way of
aggregating
different sources. The main academic and industry sources are listed in the end of the
chapter.
The costing is expressed at two different levels:
- The equipment cost, as it says, includes the main equipment and basic
balance of plant.
The costing (€/kW or $/kW) equation is function of the nominal power of the compressor
- The total cost represents the sum of the equipment cost and the
auxiliary costs.
The latter can be significative, it includes an estimation of engineering, civil works,
transportation, instrumentation and piping costs. Total cost is expressed as a range,
with a
low and a high estimations both calculated as a percentage (%) of the equipment cost.
The low estimate of the total compressor cost is set to a sum of the equipment cost plus
an additional 80%. The high estimate of the total cost includes the
equipment
cost plus an additional 160%.
Note that the total cost doesn't include contingencies and owner's costs.
HyJACK compressor cost estimation equation
Equipment cost (€/kW) = 75 700 x power-0.62
Cost Customisation
The equipment cost can be estimated with user given data specifying the unitary cost in “customisable parameters” (in €/kW or $/kW). While the equipment cost will be estimated based on the user given input, the total cost will be mechanically adjusted to include the addional costs of 80% / 160% (low/high estimate).
Results accuracy
A grade is added to each technology to reflect the accuracy and precision of the results. Each compressor type is recommended for a certain range of pressures and flow rates.
A grade of “Accurate Estimation” (3/3) is given if the compressors are used in the recommended ranges. For this technology and sizing, the data available is sufficient to consider the costing used for the pre-feasibility evaluations.
A grade of “Projected Estimation” (2/3) is given to reflect that the costing computed might rely on insufficient sources for this technology and sizing. The lack of data may reflect either that the technology is still under development and thus the results are projections of reachable costs in the future or the sizing computed doesn't correspond to a configuration where this technology is usually deployed.
A grade of “Enhanceable Estimation” (1/3) is given to reflect that the costing computing might rely on an insufficient number of sources for this technology and sizing. To enhance the costing for this configuration, your feedback is welcome.
For the centrifugal compressor, it is not recommended to use it for a discharge pressure higher than 800
bar or less than 1 bar. It is also not recommended to use it for a flow rate higher than 200,000 m^3/hr or less than 1500 m^3/hr.
For the reciprocating piston and diaphragm compressors, it is not recommended to use these
compressors for a discharge pressure higher than 3500 bar or less than 10 bar. It is also not recommended
to use them for a flow rate higher than 20,000 m^3/hr.
For the three compressors, a grade of “Accurate Estimation” (3/3) is given unless the compressor is
used outside the recommended range and a grade of “Projected Estimation” (2/3) is given in that case.
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The cost curves here represent a fair estimate of the average price. Given the
diversity of
suppliers and the product standardisation being still in its early stages, there
remains a
significant dispersion of actual prices between suppliers and projects.
Optimal calibration of the asset with the exact outputs goes beyond the
scope of this
platform. Precise engineering and costing should be subject to case-by-case
discussion with the suppliers.
Sources
REPORTS:
- NREL (2014) Hydrogen Station Compression, Storage, and Dispensing Technical Status and Costs
- Strategic Analysis Inc. (2016) Final Report: Hydrogen Storage System Cost Analysis
- Handbook of Reliability Prediction Procedures of Mechanical Equipment (2011)
SCIENTIFIC PAPERS:
- G.Sdanghi and al. Review of the current technologies and performances of hydrogen compression for stationary and automotive applications (2019)
- Sofoklis Makridis (2016) Methane and Hydrogen for Energy Storage (pp.1-28) Edition: 1 Chapter: 1 Publisher: IET Digital Library
