||A one-million ton hot iron per year suspension ironmaking plant has been simulated with the consideration of activity coefficient of FeO in slag by using Metsim simulation software package for calculating material balance and energy balance in this thesis. Mathematical models found in the literature for calculating the activity coefficient of FeO in slag were first selected, reviewed and assessed. Park and Lee's regular solution model was evaluated to be the most appropriate model for this study, and was integrated with the Metsim simulation software for the simulation of the suspension ironmaking process. Six suspension ironmaking processes were simulated: one-step process with pure H2, two-step process with pure H2, one-step reformerless process with natural gas, two-step reformerless process with natural gas, one-step process with SMR-H2 and one-step process with SMR-syngas. The simulated results show that the suspension ironmaking processes with pure H2 and reformerless natural gas are more energy efficient than conventional blast furnace ironmaking process, mainly due to the direct use of iron ore concentrate and no need for coke in the suspension ironmaking processes. The reformerless suspension ironmaking process with natural gas would consume 30 - 41% less energy than the average blast furnace ironmaking process. On the basis of material balance and energy balance, the economical feasibility of the suspension ironmaking process was analyzed. Capital cost, operating cost, CO2 credit and net present value were used in analyzing economic feasibility of the suspension ironmaking process. The analyzed results show that pure H2 process would require the least capital cost and receive the largest CO2 credit, but need the highest operating cost. Even without considering CO2 credit, except pure H2 process, all other suspension ironmaking processes would be profitable with positive NPV values. With sufficient CO2 credit, all suspension ironmaking processes simulated would be profitable, among which reformerless natural gas would return the best economics. Capital cost for the one-million ton per year suspension ironmakng plant with reformerless natural gas would be $414 million for one-step and $537 million for two-step, operating cost $429/tHI and $418/tHI, and NPV $333/tHI and $177/tHI without CO2 credit and $813/tHI and $795/tHI with $100/t CO2 credit, respectively. Economic sensitivity was also analyzed. Lower fuel price, lower operating cost, higher hot iron price and larger CO2 credit would all help improve the economics of the suspension ironmaking process.