Steady-State Operational Degrees of Freedom with Application to Refrigeration Cycles

Jensen, Jørgen Bauck; Skogestad, Sigurd

doi:10.1021/ie800565z

Cited by 26 publications

(7 citation statements)

References 14 publications

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“…The number of actual degrees of freedom (DOF), (N ss ), can be calculated by subtracting the number of DOF without steady-state effect, (N 0 ), from the number of dynamic manipulated variables, (N MV ). 11 Hence, N ss 5 N MV 2 N 0 . The C 3 MR liquefaction cycle used in this study has 11 N MV as follows: a.…”

Section: Degrees Of Freedommentioning

confidence: 96%

“…One NG feed valve (1) b. Two choke valves for the MR cycle (2) and (3) c. One common speed variable for the MR compressors (4) d. Flow of cooling medium for the MR compressor coolers (5) and (6) e. Flow of cooling medium in the propane precooled MR cooler (7) f. Two spillback valves (8) and (9) g. Two release valves of knock-out drums (10) and (11) No liquid level needs to be controlled in the recycle loop (N 0 5 0), so N ss 5 11.…”

Section: Degrees Of Freedommentioning

confidence: 99%

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Control structure synthesis for operational optimization of mixed refrigerant processes for liquefied natural gas plant

Husnil

Lee

2014

AIChE Journal

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The best control structures for the energy optimizing control of propane precooled mixed refrigerant (C 3 MR) processes were examined. A first principles-based rigorous dynamic model was developed to analyze the steady-state and dynamic behaviors of the C 3 MR process. The steady-state optimality of the C 3 MR process was then examined in a whole operation space for exploring the feasibility of the energy optimizing control for possible control structures. As a result, the temperature difference (TD) between the warm-end inlet and outlet MR streams was exploited as a promising controlled variable to automatically keep the liquefaction process close to its optimum. The closed-loop responses were finally evaluated for every possible control structure candidate. Based on the steady-state optimality and the dynamic performance evaluation, several control structures with a TD loop were proposed to be most favorable for the energy optimizing control of the C 3 MR process. The proposed optimality approach can be applied to any natural gas liquefaction process for determining a proper controlled variable for optimizing operation.

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Section: Degrees Of Freedommentioning

confidence: 96%

Section: Degrees Of Freedommentioning

confidence: 99%

Control structure synthesis for operational optimization of mixed refrigerant processes for liquefied natural gas plant

Husnil

Lee

2014

AIChE Journal

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“…Further, Jensen and Skogestad proposed a control structure to minimize the cost during operation of the PRICO process. Jensen and Skogestad focused on determining the degrees of freedom for optimal operation and plant-wide control. The steady-state degrees of freedom available for optimization are very important, because they determine the number of free variables available to solve the optimization problem as well as how many steady-state controlled variables must be selected to operate the process.…”

Section: Research On the Liquefaction Processesmentioning

confidence: 99%

Current Status and Perspectives of Liquefied Natural Gas (LNG) Plant Design

Lim

Choi²,

Moon

2013

Ind. Eng. Chem. Res.

236

123

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Liquefied natural gas (LNG) is attracting great interest as a clean energy alternative to other fossil fuels, mainly due to its ease of transport and low carbon dioxide emissions, a primary factor in air pollution and global warming. It is expected that this trend in the use of LNG will lead to steady increases in demand over the next few decades. To meet the growing demand for LNG, natural gas liquefaction plants have been constructed across the globe. Furthermore, single train capacity has been increased to strengthen price competitiveness. To achieve greater capacity, more complex refrigeration cycle designs that combine two or more different conventional single refrigeration cycles are being developed to obtain synergistic effects in the liquefaction process. At the same time, a variety of recent studies have focused on designing suitable processes for offshore and small-scale plants to improve the profitability of stranded gas fields. LNG plants are known to be energy/cost-intensive, as they require a large amount of power for the processes of compression and refrigeration, and need special equipment such as cryogenic heat exchangers, compressors, and drivers. Therefore, one of the primary challenges in the LNG industry is to improve the efficiency of the current natural gas liquefaction processes in combination with cost savings. In this paper, we review recent developments in LNG processes, with an emphasis on commercially available refrigeration cycles. We also discuss recent research and suggest future directions for natural gas liquefaction processes. Up to this point, most studies have focused on operating cost. To achieve better results, future studies that investigate optimal design and operation of LNG technologies should consider both capital cost and operating cost.

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“…The generator is fired through a heat transfer fluid, in this case thermal oil, exchanging heat with the rich solution. The poor solution is picked up by a tube (13) and sent to the solution cooled absorber after passing through an expansion valve (14). In the solution cooled absorber, the ammonia depleted solution drips over the tube coil while absorbing vapor refrigerant and is collected in the bottom of the tank.…”

Section: Plant Descriptionmentioning

confidence: 99%

“…In [14] some examples for the systematic calculation of the degrees of freedom for compression refrigeration chillers are presented, but the case of absorption chillers is not included. We now concentrate on the model.…”

Section: Absorption Chiller Modeling and Data Reconciliation Approachmentioning

confidence: 99%

Performance Analysis of Absorption Chillers Using Data Reconciliation

Martinez

Bruno

Bagajewicz

et al. 2010

ASME 2010 10th Biennial Conference on Engineering Systems Design and Analysis, Volume 1

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Performance data obtained from measurements of process variables usually do not obey material and energy conservation laws. This is why a data reconciliation process, that is, the adjustment of measured data to obey the conservation laws and other constraints is necessary in order to characterize the real performance of equipment, processes, or the whole plant. The information on the partial load and off-design operation performance of absorption chillers is scarce. Real operation of these units do not always coincides with the expected performance according to the data provided by the manufacturer due to site specific conditions. On the other hand the data reconciliation procedure has been extensively applied mainly only for open cycles with a moderate number of recycle streams. The objective of this work is the development and application of the data reconciliation technique to analyse the performance of absorption chillers using rigorous thermodynamic properties for the calculation of the P-V-T equilibrium properties and enthalpies. We present in this paper the preliminary test results for one of the absorption chiller components, the evaporator.

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Steady-State Operational Degrees of Freedom with Application to Refrigeration Cycles

Cited by 26 publications

References 14 publications

Control structure synthesis for operational optimization of mixed refrigerant processes for liquefied natural gas plant

Control structure synthesis for operational optimization of mixed refrigerant processes for liquefied natural gas plant

Current Status and Perspectives of Liquefied Natural Gas (LNG) Plant Design

Performance Analysis of Absorption Chillers Using Data Reconciliation

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