Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Undoubtedly, a nice piece of technical study - a strong PhD thesis.  The strong authorship practically ensures that.  Personally, it tells me nothing new, but it may be enlightening to novices in the field.  I am not going to quibble about the CAPEX estimations and economic analysis.  To those of us who are doing those evaluations in the course of our business, those numbers are truly meaningless and/or misleading.  So far, for novel technologies, actual project experience tells us that after a AACE Class 3 or higher FEED study, the numbers that we are looking at are at least 2-3 times those found in academic literature.

My true recommendation for this manuscript is "major revision".  Having said that I would not be terribly disappointed if it is published with minor revisions.  As I mentioned above, it is pretty sound work.  I cannot reproduce the entire thermodynamic cycle analysis, but the numbers I see in Table 6 are basically in line with expectations (efficiencies that is; I have a hard time buying into ~900 MW IRWI gas turbine).

However, as is, this paper adds not much to the technical literature.  The isothermal turbine is nothing new.  What can a reader learn from this paper that s/he cannot figure out from El-Masri's papers?

The IRWI cycle is essentially a variation on late Dr. Nakhamkin's CHAT technology.  The paper is completely mute on this cycle.  This glaring omission must be rectified in the Intro and References.

What about R-R's WR-21 intercooled-recuperated marine gas turbine engine.  This is an actually built and operated (distant) relative of IRWI and deserves at least a mention.

Historical examples of intercooled and recuperated (plus reheat) gas turbine power plants (by GE, Brown & Boveri) have been built and operated.  What led to their demise? Today's 1x1x1 50-Hz GTCC with a 500+ MW gas turbine is nearly 800 MW at full load, can run at 200 MW MECL, start in 30 minutes (or less), and ramp up/down fast and serve in frequency response duty.  Can these gas turbines? How?  These issues must be discussed.

My recommendation for this paper is the following:

1. Skip the modeling part.  Put it into a supplementary document for reference.  We are convinced that the authors CAN model gas turbines.  While, for these types of studies, I personally am adamantly against "homemade" codes and insist on using established commercial software (Thermoflow Inc., SoftInWay, etc.), I can let go of it for this particular crew.

2. Skip the extensive economic analysis and cost estimation.  After the technical comparison in Table 6, do this "what if" study: NGCC (base case) is well known to cost $X ($X times a suitable factor with PCC). Under what CAPEX, OPEX, H2 cost, and CO2 penalty assumptions the proposed technologies would have a fighting chance vis-a-vis advanced class GTCC?

This is the key question to answer.

3. Most important: Dedicate the saved space to operability considerations.  (BTW, the statement "Technically speaking, CO2 capture plants can achieve flexibility via strategies such as venting CO2 instead of capturing it when power demand is high." is incorrect and/or incomplete.  There are patents and papers out there describing that capture can continue at times of high demand and rich amine is stored with the stripper/regenerator down.  It can be operated later to clean the stored rich amine and remove CO2.)

These multi-shaft units will have significant control, ramp up/down, startup/shutdown, etc. issues.  Their thermodynamic performance modeling is trivial.  The authors should research the existing technology and discuss how the hardware implementation of these cycles (beyond the combustion issues) can impact their configuration and/or performance.

GTCC reached 60+% efficiency mark after a half century of intense R&D and commercial deployment.  Some predictions must be made about the life cycle projections of these cycles.  This is where the authors can really make a contribution to the technical literature.

If need be, OEMs should be consulted for some of the answers.

4. Some equipment sizing considerations must be discussed.  A 900+ MW IRWI is hard to design, build, and operate.  How?

Author Response

Please see the attachment. 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Overview

The manuscript elaborates on how variable renewable energy sources can be incorporated by devising novel steps that integrate a near-isothermal hydrogen turbine (NIHT) cycle and an intercooled recuperated water-injected (IRWI) cycle. The study presents an extensive techno-economic evaluation of these cycles and their capability to be cost-effective even at lower capacity factors, which is very important for wind and solar-renewable systems.

Strengths

1.     Innovative Concepts: The NIHT and IRWI cycles have been introduced in an innovative manner since their objective is to cut down the capital cost, while optimizing on the high efficiency. Enhance of near-isothermal expansion by NIHT and effective recovery of waste heat by IRWI without complicated bottoming cycles have been some good improvements.

2.     Comprehensive Analysis: The manuscript contains a thorough moderation – economic, technical, including technical and economic modeling of systems operating with hydrogen as well as natural gas. The analysis of fuel supply costs and how they affect the levelized cost of electricity (LCOE) is important and most studies do not include that.

3.     Technical Depth: The technical modeling is extensive and uses high-level tools for simulation like Unisim Design and Politecnico di Milano GS code. The blade cooling flow model and calibration regression using H-class gas turbine parameters form a solid platform for the proposed cycles.

4.     Figures and Data Presentation: The authors could articulate clearly the results by appropriate use of figures and tables. For example, the efficiency comparisons, LCOE analyses and fuel price sensitivity are well presented in order to support the findings of this paper.

Major Comments

1.     Validation and Experimental Data:

Although the manuscript is based much on simulations, the authors fail to validate the NIHT and the IRWI cycles through experiments. For example, some experimental data, if available, would let showcasing the attained results in a more credible way.

2.     Detailed Explanation of Novelty:

A more detailed comparison with existing cycles would show clearly the advancements offered by these novel cycles.

3.     Handling of Hydrogen-Fuelled Scenarios:

The economic assessment indicates that a hydrogen fuelled power station could be viable within certain limiting conditions. But only, the manuscript shows, the hydrogen price is a very sensitive issue. It would be useful to add here recommendations on how to resolve the problem of the high capital required for hydrogen storage and transportation, perhaps suggesting using dispersed production of hydrogen.

4.     Impact of Assumptions on Results:

There are several assumptions related to some factors such as: capital cost assumptions, efficiency values, distances for fuels supply and so on. An appropriate model needs to be developed to incorporate the effect of these assumptions, in particular.

5.     Technological Challenges:

The manuscript attempts to address the technological challenges as follows: TMU is aiming at carrying out fuel injection accurately in the NIHT as well as the problems of the material due to high temperatures. These challenges could be studied further, including how they could be solved or what is being done to address them.

6.     Environmental Impact:

There is a limited mention with respect to other environmental factors other than CO₂ emissions. Since the manuscript discusses hydrogen and natural gas usage, consideration of the wider environmental issues including NO_x emissions or water used in the IRWI cycle should extend the perspective provided.

Minor Comments

1.     Clarity in Diagrams:

Some diagrams can be improved by adding annotations for an enhanced readability such as the T-s diagram and the process flowcharts.

2.     Reference Updates:

Some references are outdated or insufficiently cited, and it is important to ensure that the manuscript incorporates the most recent and relevant research. It is recommended to replace the outdated ones with more recent ones.

3.     Consistency in Units:

There should be consistency in using units (e.g., economic analysis sections).  For example, €/GJ and €/MWh are being used interchangeably, and this negatively affects the quality of the result presentation and analysis.

 

4.     Typographical and Formatting Errors:

It is recommended to proofread the manuscript by an English expert to avoid grammatical and typographical errors and enhance the quality of writing.

Final Decision

Accepted with major revisions.

 

Comments on the Quality of English Language

It is recommended to proofread the manuscript by an English expert to avoid grammatical and typographical errors and enhance the quality of writing.

Author Response

Please see the attachment. 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Good paper.  Thanks.

Reviewer 2 Report

Comments and Suggestions for Authors

After thoroughly reviewing the revised manuscript, I have no further comments. I fully endorse the manuscript in its current form and approve it for publication.