1-dimensional modelling and simulation of the calcium looping process

Calcium looping is an emerging technology for post-combustion carbon dioxide capture and storage in development. In this study, a 1-dimensional dynamical model for the calcium looping process was developed. The model was tested against a laboratory scale 30 kW test rig at INCAR-CSIC, Spain. The study concentrated on steady-state simulations of the carbonator reactor. Capture efficiency and reactor temperature profile were compared against experimental data. First results showed good agreement between the experimental observations and simulations

Modeling of the oxy-combustion calciner in the post-combustion calcium looping process

The calcium looping process is a fast-developing post-combustion CO2 capture technology in which combustion flue gases are treated in two interconnected fluidized beds. CO2 is absorbed from the flue gases with calcium oxide in the carbonator operating at 650 ºC. The resulting CaCO3 product is regenerated into CaO and CO2 in the calciner producing a pure stream of CO2. In order to produce a suitable gas stream for CO2 compression, oxy-combustion of a fuel, such as coal, is required to keep the temperature of the calciner within the optimal operation range of 880-920°C. Studies have shown that the calcium looping process CO2 capture efficiencies are between 70 % and 97 %. The calciner reactor is a critical component in the calcium looping process. The operation of the calciner determines the purity of gases entering the CO2 compression. The optimal design of the calciner will lower the expenses of the calcium looping process significantly. Achieving full calcination at the lowest possible temperature reduces the cost of oxygen and fuel consumption. In this work, a 1.7 MW pilot plant calciner was studied with two modeling approaches: 3-D calciner model and 1-D process model. The 3-D model solves fundamental balance equations for a fluidized bed reactor operating under steady-state condition by applying the control volume method. In addition to the balance equations, semiempirical models are used to describe chemical reactions, solid entrainment and heat transfer to reduce computation effort. The input values of the 3-D-model were adjusted based on the 1-D-model results, in order to model the behavior of the carbonator reactor realistically. Both models indicated that the calcination is very fast in oxy-fuel conditions when the appropriate temperature conditions are met. The 3-D model was used to study the sulfur capture mechanisms in the oxy-fired calciner. As expected, very high sulfur capture efficiency was achieved. After confirming that the 1-D model with simplified descriptions for the sorbent reactions produces similar results to the more detailed 3-D model, the 1-D model was used to simulate calcium looping process with different recirculation ratios to find an optimal area where the fuel consumption is low and the capture efficiency is sufficiently high. It was confirmed that a large fraction of the solids can be recirculated to both reactors to achieve savings in fuel and oxygen consumption before the capture efficiency is affected in the pilot unit. With low recirculation ratios the temperature difference between the reactors becomes too low for the cyclic carbonation and calcination. As a general observation, the small particle size creates high solid fluxes in the calcium looping process that should be taken into account in the design of the system

Predictors of mortality at one year after generalized convulsive status epilepticus

Background: Status epilepticus (SE) is a life-threatening neurologic emergency, which requires prompt medical treatment. Little is known of the long-term survival of SE. The aim of this study was to investigate which factors influence 90 days and 1-year mortality after SE. Materials and methods: This retrospective study includes all consecutive adult (>16 years) patients (N = 70) diagnosed with generalized convulsive SE (GCSE) in Helsinki University Central Hospital (HUCH) emergency department (ED) over 2 years. We defined specific factors including patient demographics, GCSE characteristics, treatment, complications, delays in treatment, and outcome at hospital discharge and determined their relation to 90 days and 1-year mortality after GCSE by using logistic regression models. Survival analyses at 1 year after GCSE were performed with Cox proportional hazards regression analysis. Results: In-hospital mortality was 7.1%. Mortality rate was 14.3% at 90 days and 24.3% at 1 year after GCSE. In the univariate logistic regression analysis, Status Epilepticus Severity Score > 4 (STESS) (ODDS = 7.30, p = 0.012), worse-than-baseline condition at hospital discharge (ODDS = 3.5, p = 0.006), long delays in attaining seizure freedom (ODDS = 2.2, p = 0.041), and consciousness (ODDS = 3.4, p = 0.014) were risk factors for mortality at 90 days whereas epilepsy (ODDS = 0.2, p = 0.014) and Glasgow Outcome Scale (GOS) > 3 at hospital discharge (ODDS = 0.05, p = 0.006) were protective factors. Risk factors for mortality at 1 year were STESS >4 (ODDS = 5.1, p = 0.028), use of vasopressors (ODDS = 8.2, p = 0.049), and worse-than-baseline condition at discharge (ODDS = 7.8, p = 0.010) while GOS >3 (ODDS = 0.2, p = 0.005) was protective. The univariate survival analysis at 1 year confirmed the significant findings regarding parameters STESS >4 (Hazard ratio (HR) = 4.1, p = 0.009), worse-than-baseline condition (HR = 6.2, p = 0.015), GOS >3 (HR = 0.2, p = 0.004) at hospital discharge and epilepsy (HR = 0.4, p = 0.044). Additionally, diagnostic delay over 6 h (HR = 3.8, p = 0.022) and Complication Burden Index (CBI) as an ordinal variable (0-2, 3-6, >6) (HR = 2.7, p = 0.027) were predictive for mortality. In the multivariate survival analysis, STESS > 4 ( HR = 5.1, p = 0.007), CBI (HR = 3.2, p = 0.025, ordinal variable), diagnostic delay over 6 h (HR = 7.2, p = 0.003), and worse-than-baseline condition at hospital discharge (HR = 5.8, p = 0.027) were all independent risk factors for mortality at 1 year. Conclusions: Severe form of SE, delayed recognition of GCSE, high number of complications during treatment period, and poor condition at hospital discharge are all independent predictors of long-term mortality. Most of these factors are also associated with mortality at 90 days, though at that point, delays in treatment seem to have a greater impact on prognosis than at 1 year. This article is part of the Special Issue "Proceedings of the 7th London-Innsbruck Colloquium on Status Epilepticus and Acute Seizures (c) 2019 Elsevier Inc. All rights reserved.Peer reviewe

Delays and Factors Related to Cessation of Generalized Convulsive Status Epilepticus

Peer reviewe

Burden of suspected epileptic seizures on emergency services : A population-based study

Background and purposePatients with acute epileptic seizures form a large patient group in emergency neurology. This study aims to determine the burden caused by suspected epileptic seizures at different steps in emergency care.MethodsA retrospective, cross-sectional, population-based (>1,000,000 inhabitants), 4-year (2015-2018) study was conducted in an urban setting with a single dispatch centre, a university hospital-affiliated emergency medical service (EMS), and five emergency departments (EDs). The study covered all adult (>= 16 years old) emergency neurology patients receiving medical attention due to suspected epileptic seizures from the EMS and EDs and during hospital admissions in the Helsinki metropolitan area.ResultsEpileptic seizures were suspected in 14,364 EMS calls, corresponding to 3.3% of all EMS calls during the study period. 9,112 (63.4%) cases were transported to hospital due to suspected epileptic seizures, and 3368 (23.4%) were discharged on the scene. 6969 individual patients had 11,493 seizure-related ED visits, accounting for 3.1% of neurology- and internal medicine-related ED visits and 4607 hospital admissions were needed with 3 days' median length of stay (IQR=4, Range 1-138). Male predominance was noticeable at all stages (EMS 64.7%, EDs 60.1%, hospital admissions 56.2%). The overall incidence was 333/100,000 inhabitants/year for seizure-related EMS calls, 266/100,000 inhabitants/year for ED visits and 107/100,000 inhabitants/year for hospital admissions. Total estimated costs were 6.8 million euro/year, corresponding to 0.5% of all specialized healthcare costs in the study area.ConclusionsPatients with suspected epileptic seizures cause a significant burden on the health care system. Present-day epidemiological data are paramount when planning resource allocation in emergency services.Peer reviewe

Burden of suspected epileptic seizures on emergency services:a population-based study

Abstract Background and purpose: Patients with acute epileptic seizures form a large patient group in emergency neurology. This study aims to determine the burden caused by suspected epileptic seizures at different steps in emergency care. Methods: A retrospective, cross-sectional, population-based (>1,000,000 inhabitants), 4-year (2015–2018) study was conducted in an urban setting with a single dispatch centre, a university hospital-affiliated emergency medical service (EMS), and five emergency departments (EDs). The study covered all adult (≥16 years old) emergency neurology patients receiving medical attention due to suspected epileptic seizures from the EMS and EDs and during hospital admissions in the Helsinki metropolitan area. Results: Epileptic seizures were suspected in 14,364 EMS calls, corresponding to 3.3% of all EMS calls during the study period. 9,112 (63.4%) cases were transported to hospital due to suspected epileptic seizures, and 3368 (23.4%) were discharged on the scene. 6969 individual patients had 11,493 seizure-related ED visits, accounting for 3.1% of neurology- and internal medicine-related ED visits and 4607 hospital admissions were needed with 3 days’ median length of stay (IQR=4, Range 1-138). Male predominance was noticeable at all stages (EMS 64.7%, EDs 60.1%, hospital admissions 56.2%). The overall incidence was 333/100,000 inhabitants/year for seizure-related EMS calls, 266/100,000 inhabitants/year for ED visits and 107/100,000 inhabitants/year for hospital admissions. Total estimated costs were 6.8 million €/year, corresponding to 0.5% of all specialized healthcare costs in the study area. Conclusions: Patients with suspected epileptic seizures cause a significant burden on the health care system. Present-day epidemiological data are paramount when planning resource allocation in emergency services