(769a) Evaluation of Reclaimer Sludge Disposal Options From Amine-Based Post-Combustion CO2 Capture Process
AIChE Annual Meeting
Friday, November 8, 2013 - 8:30am to 8:55am
An important environmental issue with respect to amine-based post-combustion CO2 capture is the generation of amine waste containing degradation products and system impurities that must be mitigated or disposed of properly. The operation of an amine-based post-combustion CO2 capture process will result in the formation of degradation products due to the presence of oxygen, NOx and SOx in the flue gas; additional impurities present in the flue gas (heavy metals, fly ash, halogen compounds) can be physically absorbed into the solvent and accumulate as it circulates within the CO2capture system.
These degradation products exhibit corrosive properties and reduce solvent CO2 absorption characteristics. To control the concentration of these degradation products in the amine- based solvent, a slipstream of the solvent from the CO2 capture unit is sent to a solvent reclaiming system; the recovered amine-based solvent is returned to the CO2capture unit, while waste from the reclaimer unit is discharged for disposal/treatment. This paper evaluates the environmental fate of reclaimer waste streams generated from three common amine-based solvents: monoethanolamine (MEA) , piperazine (PZ) and a methyldiethanolamine/piperazine blend (MDEA/PZ).
Reference cases will be developed for the supercritical pulverized coal (PC) and natural-gas combined cycle (NGCC) power plants at their respective gross power outputs, along with reference cases for the CO2 capture processes integrated with the power facilities. These reference cases will identify the lean/rich loadings and circulation rate of the solvents of interest, in addition to the operating conditions of the regeneration column (used to characterize thermal degradation rates). Commentary will be provided on oxygen and trace impurities concentrations in the flue gas, and how these concentrations affect impurities and degradation product concentration within the circulating amine solvent adjusted to the overall CO2capture rate. For other solvent systems (PZ, AMP/PZ, amino acids, etc.) where data are readily available, a qualitative analysis of degradation information will be provided.
For each solvent system, a degradation model will be developed to estimate solvent loss, impurities accumulation and degradation product accumulation expected in a commercial CO2 capture unit. Solvent losses are expected via thermal degradation, oxidative degradation, amine volatility, reclaimer operation, nitrosamine formation from NOx, and reactions with flue gas impurities. Thermal degradation losses will be modeled as a function of regeneration operating temperature and pressure, as well as rich loading of the amine-based solvent, while oxidative degradation losses will be modeled as a function of oxygen concentration, dissolved metal ion concentration and rich loading of the amine-based solvent. Reclaimer solvent losses will be modeled as a function of reclaimer inlet composition (includes degradation product and heavy metals concentrations) and reclaimer operating conditions. Solvent losses from flue gas impurities will be modelled as a function of impurities concentrations in the flue gas and the rate of physical absorption of the individual impurities.
A technology feasibility and economic analysis of various reclaiming technologies (e.g., thermal and vacuum distillation, ion exchange, and electrodialysis) will be conducted for each solvent system; the analysis will include process descriptions, process flow diagrams, steady-state mass balances, energy requirements, utility requirements, equipment lists, costs and projected solvent losses. Reported economic metrics will include the levelized cost of electricity (LCOE) and cost of CO2emissions avoided; energy requirements for each reclaiming process will be normalized in terms of kW/gallon of solvent reclaimed.
Key assumptions within the analysis include the expected composition of reclaimer feed, typical amine recovery in a thermal reclaiming system, recovery of amine impurities and degradation products from the amine solvent, and the fraction of amine degradation that occurs during thermal reclaiming. These assumptions will be developed from information gathered from journals, conference proceedings, conversations with amine waste treating industry representatives, and conversations with reclaiming vendors. In addition, conversations with reclaiming vendors and amine waste treating industry representatives will be used to better understand operating experiences and operating preferences depending upon the composition of the inlet gas stream being treated and operating conditions within the amine treating system.
The composition of the reclaimer waste generated from each solvent via each type of reclaimer technology will be estimated and then classified based on US and EU environmental regulations for hazardous waste; in addition, cursory evaluations will be performed based on regulations in the UK, Canada and Australia. The evaluation will include extracting specifically applicable sections and sub-sections of pertinent regulations and discussing how they might apply to the reclaimer waste. Specifically, heavy metals will be evaluated, and concentrations that trigger hazardous waste regulations will be specifically identified.
This paper will also evaluate several potential options for disposing the reclaimer sludge waste, such as conventional incineration, co-firing in a power plant boiler, use as an SNCR reagent, treating in a conventional wastewater treatment plant, and use in a cement kiln. For each option, regulatory and technical feasibility, potential extra processing that would be required, and indication of the relative costs will be provided.
Based upon the tasks mentioned, recommendations will be developed to identify optimal operating conditions to minimize solvent loss and to identify the main components of the reclaimer waste expected from the specified flue gas composition and capture conditions. In addition, a review of existing and foreseeable issues of reclaiming with likely capture solvents will be conducted to provide direction for future research and development of other advanced reclaiming concepts and waste disposal.
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