ASPEN PLUS
ASPEN PLUS is a software that predicts the performance of processes in thermodynamic models. With this software, I have been able to simulate processes, with the goal to optimize designs.
RANKINE CYCLE
Flowsheet of Rankine cycle model with R22 as working fluid
Sensitivity analysis Efficiency vs. Pump ratio
Table of varied parameters and dependent parameters
The objective of this simple Ranking cycle model was to put into practice the efficiency and net work equations in an analysis computed by ASPEN. For this reason, the setup of the blocks and streams assumed ideal conditions that wouldn’t be realistic in a real life Thermodynamic cycle.
The vapor fraction in the condenser is 0 and the vapor fraction in the heater is 1. In the pump, the pressure ratio is 2, and the isentropic efficiency is 0.85. For the turbine, the discharge pressure is 1 bar, and the isentropic efficiency is 0.9. Finally, the stream LPVAP is set to 20ºC, 1 bar, and mass flow 100 kg R22/hr.
As the pump ratio increases, the cycle efficiency also increases in approximately a linear trend. This is because a higher pump ratio will yield the fluid (R22) at a higher pressure.
This causes the pump(Win) power, the turbine(Wout) power and the heat input (Qin) to increase. However, the turbine work is the value that increases the most (as seen in the table below), causing an increase in the net cycle work. This will cause the efficiency increase as efficiency =Wnet/Qin
COAL AND BIOMASS GASIFICATION
In this analysis computed with ASPEN, I compared the data of coal gasification of an Upper Freeport (UF) bituminous coal to the gasification of biomass (Douglas Fir) and one of the lower rank coals in Argonne Premium summer bank.
Sensitivity analysis of UF coal with O2 flow rate of 700-1500 kg/hr
Sensitivity analysis of Douglas Fir with O2 flow rate of 500-1000 kg/hr
Sensitivity analysis of WY coal with O2 flow rate of 500-1000 kg/hr
Discussion : How do the differences in fuel composition and HHV affect the product gas (especially H2) yields for the three samples
From the three sensitivity analysis, we can clearly see the difference of product gas yields when changing the fuel composition and varying the oxygen flow rate.
Firstly, we can see that UF coal and WY coal act more similarly, as they have a more similar fuel composition. Both of them have a general trend of increasing levels of hydrogen, carbon monoxide and carbon dioxide, while the level of methane gas decreases. On the other hand, for Douglas Fir as the oxygen flow rate increases, yields an increasing level only for carbon dioxide, while hydrogen, carbon monoxide and methane values decrease.
As to the specific evolution of hydrogen for the three fuels, the level in Douglas Fir starts high at 40.5kg/hr and constantly decreases. For UF coal and WY coal we see the opposite trend. They both have a low starting hydrogen level (around 0.5 kg/hr), and then it increases. UF coal has its hydrogen peak value of 24 kg/hr at an oxygen flow rate of 1300 kg/hr, and WY coal has its hydrogen peak value of 27.5 kg/hr at an oxygen flow rate of 800 kg/hr.
Moreover, we can also link the difference in yield product rates to the different HHV values. The highest heating value corresponded to Douglas Fir (21050 kJ/kg), then UF coal (20,000 KJ/kg) and finally WY coal (19,590 KJ/kg). If we compare the two similar compositions, WY coal and UF coal, we can see that a higher heating value will delay the moment of peak hydrogen, therefore needing a higher oxygen flow rate. This is why UF coal, which has a higher heating value, had its hydrogen peak much later that WY coal.
As the flow rate of oxygen increases, we can see the product gasses severely change. As an observation, the products of hydrogen, carbon monoxide and carbon dioxide, have a final flow rate higher than their starting value. On the other hand, methane finishes with a lower flow rate (600 kg/hr) than what it started.
Hydrogen and carbon monoxide increase until its maximum value when the oxygen flow rate is 1300 kg/hr, and then decrease.
Methane and carbon dioxide increase until 800 and 900 kg/hr respectively, and then decrease until 1400 and 1300 kg/hr off oxygen flow rate.