Characterization of Ammonia-Water Absorption Chiller and Application

Gopalakrishnan Anand,Donald C Erickson,Ellen Makar 대한설비공학회 2018 International Journal Of Air-Conditioning and Refr Vol.26 No.4

Ammonia-absorption refrigeration units (AARUS) can supply subfreezing refrigeration for many industrial applications. Such units are usually driven by waste heat or renewable energy at relatively low temperatures. The performance of the chiller is highly dependent on the temperatures of the driving heat, the chilling load, and the cooling water. In this paper, the performance of an advanced industrial-scale ammonia-absorption unit is modeled over a representative operating range. The performance is then characterized by a set of simple equations incorporating the three external temperatures. This simple model helps to evaluate potential applications, predict performance, and perform initial optimization. Case studies are presented highlighting the application of the model.

Subfreezing Absorption Refrigeration for Industrial CHP

Gopalakrishnan Anand,Donald C Erickson,Ellen Makar 대한설비공학회 2018 International Journal Of Air-Conditioning and Refr Vol.26 No.4

The design and operation of an advanced absorption refrigeration unit (Thermochiller) as part of an industrial combined heat and power (CHP) system is presented. The unit is installed at a vegetable processing plant in Santa Maria, California. The overall integrated system includes the engine package with waste heat recovery, Thermochiller, cooling tower, and chilling load interface. The unique feature of the system is that both the exhaust and jacket heat are used to supply subfreezing refrigeration. To achieve the low refrigeration temperatures of interest to industrial applications, all components of this integrated system needed careful consideration and optimization. The CHP system has a low emission natural gas-fired 633kW reciprocating engine cogeneration package. Both the exhaust heat and jacket heat are recovered and delivered via a hot glycol loop with 105 ∘ C supply temperature and 80 ∘C return. The 125 ton ammonia absorption chiller (TC125) chills propylene glycol to −6 ∘ C and has a coefficient of performance of 0.63. TC125 has peak electric demand of 10 kW for pumps and 8 kW for the cooling tower fan. The CHP system, including TC125, operates 20 h per day, six days per week. All operations of TC125 are completely automatic and autonomous, including startups and shutdowns. Industrial refrigeration is typically a 24/7 load and highly energy-intensive. By converting all the engine waste heat to subfreezing refrigeration, Thermochiller brings added value to cogeneration or CHP projects.

Chilled Coil Control and Field Performance for Turbine Inlet Air Chilling

Gopalakrishnan Anand,Ellen Makar 대한설비공학회 2021 International Journal Of Air-Conditioning and Refr Vol.29 No.2

Ambient conditions greatly affect the combustion turbine performance. The Absorption Refrigeration Cycle Turbine Inlet Chilling (ARCTIC) system can chill the inlet air of the turbine to maintain optimum performance at all ambient temperatures. However, turbine characteristics, bell-mouth icing concerns, economics and performance guarantees require maintaining the inlet air temperature within a narrow range throughout the year. These considerations require strict control of the Turbine Inlet Air Chilling (TIAC) coil performance over a wide range of operating conditions. This paper describes the field performance and control of the chilling coil for a Mars 100 turbine. The controls logic had been developed from previously published empirical model of the chilling coil and model of the chilling loop performance at the various ambient conditions. Since commissioning at the end of summer 2020, the ARCTIC has provided inlet air chilling over a range of ambient conditions. Typically, the inlet air is maintained at 7.2∘C (45∘F) by controlling the TIAC chilled water flow rate and temperature. On cooler days, if the inlet air temperature drops to 5.6∘C (42∘F) the chilled water pump turns OFF automatically to prevent bell-mouth icing. Thus, the chiller accommodates chilling load variations down to zero load. On colder days, the ARCTIC continues operating till the ambient temperature drops below 1.7∘C (35∘F) and then turns OFF. The chiller turns back ON when the 8 h average inlet air temperature exceeds 10∘C (50∘F). These parameters can be adjusted remotely by the operator and help maintain performance guarantees while minimizing chiller cycling. Quasi-steady state data were analyzed to quantify the chilling load and coil performance over a range of operating conditions.

Chilled Coil Performance Control and Application to Turbine Inlet Air Cooling

Gopalakrishnan Anand,Ellen Makar 대한설비공학회 2021 International Journal Of Air-Conditioning and Refr Vol.29 No.2

The Absorption Refrigeration Cycle Turbine Inlet Conditioning (ARCTIC) system can chill the inlet air of the turbine to maintain optimum turbine performance at all ambient temperatures. However, turbine characteristics and bell-mouth icing concerns impose a minimum temperature limitation on the chilled air. Performance guarantees may also require maintaining the inlet air temperature within a narrow range throughout the year. These considerations require accurate prediction of the chilling coil performance over a wide range of operating conditions and the development of a robust controls strategy. A modified wet-surface model is used to model the chilling coil performance. The application of the model to a 2110kW (600 RT) ARCTIC providing inlet air chilling for a MARS 100 turbine is considered. A control strategy is developed to maintain the inlet air temperature at the desired set point with varying ambient temperatures and chilling loads. The TIAC controls help maintain the inlet air temperature at 7.22∘C to maximize turbine capacity and efficiency during most of the hot/warm days and accommodates 100% turndown. Additional safety measures are incorporated to prevent bell-mouth icing.

Modified Chilled Coil Model Development and Application to Turbine Inlet Air Cooling

Gopalakrishnan Anand,Ellen Makar 대한설비공학회 2021 International Journal Of Air-Conditioning and Refr Vol.29 No.1

A Turbine Inlet Air Conditioning (TIAC) system can chill the inlet air of the turbine to maintain maximum turbine performance at all ambient temperatures. However, turbine characteristics, performance guarantees and bell-mouth icing considerations require accurate prediction of the chilling coil performance over a wide range of operating conditions. A modified wet-surface model (MWSM) is developed to more accurately predict the chilling coil performance. The higher accuracy of the model is demonstrated by applying the model to simulate performance data of two different coils. The data covered a wide range of operating conditions with ambient temperature vary from 43.3∘C to 9.7 ∘ C dry bulb and 27.2 ∘C to 6.1 ∘C wet bulb. The turbine flow rate varies from 100% to 43% with chilled air temperature in the range of 3.3–14 ∘ C and chilling load variation of 100% to 5%. The chilled water flow rate varies from 100% to 32% with supply glycol-water temperature in the range of −2.2–6.1 ∘ C. The MWSM uses 11 empirical parameters evaluated from the coil performance data and is able to correlate the data with an adjusted coefficient of determination (R 2 adjRadj2) of over 99%. The higher accuracy of the modified model enables the development of a more robust controls strategy required to maintain the inlet air temperature at the set point with varying ambient temperatures and chilling load conditions. The model can also be applied to other chilling and dehumidification applications especially those experiencing wide variations in operating conditions and load or those requiring close control of the chilling and dehumidification process.

Absorption Refrigeration Cycle Turbine Inlet Conditioning

Donald C Erickson,Gopalakrishnan Anand,Ellen Makar 대한설비공학회 2015 International Journal Of Air-Conditioning and Refr Vol.23 No.1

Ambient temperature markedly impacts combustion turbine performance. A typical aeroderivativeturbine loses 25% of ISO capacity at 38C ambient. There are two traditional optionsto mitigate that degradation: evaporative cooling and mechanical chilling. They boost turbineperformance, but consume signi¯cant water and/or electric load. Also, the turbine requires separateanti-icing equipment for low ambient temperature operation (less than 4.4C). This paperdescribes the Absorption Refrigeration Cycle Turbine Inlet Conditioning (ARCTIC) system thatchills or heats the inlet air of a combustion turbine to maintain maximum turbine performance atall ambient temperatures. The ARCTIC unit is an ammonia–water absorption cycle that ispowered by turbine exhaust heat. The design and performance of a 7034kW (2000-ton) ARCTICunit is presented. This ARCTIC achieved a new record for net power and heat rate from thismodel aeroderivative gas turbine in hot weather. It provides reliable and dispatchable hot daypower at about half the cost of new plant. On a typical summer day (38C dry bulb, 26C wetbulb), ammonia refrigerant from the ARCTIC chills the inlet air to 8.9C. The gas turbine poweris increased from 40 to 51MW. After allowing for the 230kW electric parasitic load, the resultingnet power is 2MW more than the output of a comparable mechanically chilled gas turbine. As aresult, the heat rate is also improved. On cold days the ARCTIC automatically switches toheating mode. The inlet air is heated by 11C to eliminate inlet icing potential. Additionalbene¯ts include a lower exhaust temperature which is better for the Selective Catalytic Reduction(SCR) catalyst. The condensate recovered from the inlet-air chilling (up to 25 gallons per minute)can also be a valuable by-product. The ARCTIC system has a small cost premium relative to amechanical chiller. However, when all the auxiliary functions are credited (anti-icing, temperingair, less switchgear, no 4160 volt service), the overall installed cost is comparable. The standoutadvantages are the increased hot weather power output, improved operating e±ciency, and reducedmaintenance, all obtained at minimal additional cost. Combined cycle and cogenerationcon¯gurations (both frame and aeroderivative) bene¯t even more from the ARCTIC due to theincreased value of improved heat rate.