CO2 corrosion control in steel pipelines. Influence of turbulent flow on the performance of corrosion inhibitors

Corrosion associated with aqueous environments containing carbon dioxide (CO₂) and/or hydrogen sulphide (H₂S), is a well-known phenomenon in oil and gas industries. This type of corrosion is of particular importance in transportation through steel pipelines. This transportation process could involve the movement of a complex mixture of gas and liquids. This moving mixture is in close contact with the inner surface of the steel pipelines and corrosion can occur. It has been demonstrated that this corrosion is influenced by flow.In oil and gas industries, film-forming corrosion inhibitors are the main tool used to control inner corrosion in pipelines. The movement of the environment generates mechanical shear stresses on the surface of the steel that can interfere with the formation of the film. This phenomenon is frequently not taken into account in corrosion control strategies and could cause problems. Despite the importance of this, there are few scientific studies available, which can provide control criteria.This work presents some ideas developed in order to understand the influence of flow on the corrosion process, making emphasis in the corrosion process associated with carbon dioxide (CO₂).     

An experimental study for H2S and CO2 removal via caustic scrubbing system

In this study, removal of hydrogen sulfide (H₂S) and carbon dioxide (CO₂) from simulated syngas has been studied on one column scrubbing system. Gas flow rate as a measure of gas residence time and superficial gas velocity, gas composition, inlet H₂S load, flow modes (countercurrent and cocurrent) and packing geometry were the parameters in the design and/or operation of an acid gas scrubber system. Better H₂S scrubbing efficiencies have been obtained in countercurrent flow mode than that of cocurrent flow mode. When accordingly designed, static mixer with its superior performance on H₂S removal overweighed to structured packings. The coexistence of CO₂ and H₂S has been shown to increase the sodium hydroxide (NaOH) consumption along the scrubber column thereby decreasing the H₂S removal efficiency at higher H₂S loads. The gas residence time as changing with the gas velocity was found to be more dominant on acid gas removal efficiency than the effect of superficial gas velocity within the experimented range. A gas residence times of equal or above 3 s were seemed to be closer to the optimum point.     

A sulfur removal and disposal process through H2S adsorption and regeneration: Ammonia leaching regeneration

An iron oxide solid sponge H₂S adsorbent works by reacting H₂S and turning ferric oxide into ferric sulfide. The ferric sulfide will be converted back into ferric oxide and elemental sulfur when contacting oxygen or air. This study investigates the leaching of elemental sulfur from the solid sponge using anhydrous liquid ammonia as solvent. The leaching treatment expectedly results in effective regeneration of the adsorbent, which is able to lead to a sulfur removal and recovery process suitable for handling the small and mid-sized sulfur production cases, i.e., those less than 10 ton/day sulfur. The leaching does not significantly impair the physical properties, including the adsorbent pellet strength. The adsorption–regeneration (or leaching) cycle could be repeated at least three times. The cumulative sulfur loading can achieve as high as 50% (w/w), three times greater than that in the one-time use. The wash-off in leaching and the spent adsorbent can be made into slurry that is to be injected into underground formations such as depleted oil wells. It is anticipated that this underground injection is safer and more efficient than acid gas injection.     

Cushioning the impact of toxic release from runaway industrial accidents with greenbelts

The three aspects of accidents in chemical process industries which cause most serious damage—explosions, fires, and toxic releases—can all be controlled to some extent if greenbelts are present around the affected industry. We have recently developed and validated a system of methodologies for greenbelt design. In this paper we present the application of these models in designing greenbelts and forecasting their role in cushioning the impact of accidental release of toxic gases. With properly located and designed greenbelts as much as 33% of the accidental release of SO₂, 43% of H₂S, and 51% of NH₃ under stable atmospheric conditions (in which the dispersion is very slow and the release thus has maximum toxic impact) can be absorbed.     

Low-dose irradiation by electron beam for the treatment of high-SOx flue gas on a semi-pilot scale—Consideration of by-product quality and approach to clean technology

Attention has been focused on the treatment of lignite-fired flue gas in order to use lignite in an environmentally friendly way – (i) low-CO₂ emission, (ii) production of a valuable by-product, (iii) no discharge of wastewater, (iv) direct removal of SO₃ (strong toxicity), and (v) treatment of high SO₂ concentration. Based on these criteria, electron beam irradiation with ammonia injection was tested on a semi-pilot scale: 800 Nm³ h^?1 flow rate, 5500 ppm SO₂, 70 ppm NO_x, 22% flue gas moisture, and 75–80 °C at the reactor outlet.As an energy-saving measure, a low dose (5 kGy) of irradiation was applied: the problem lay in the by-product quality. It is considered that (NH₄)₂SO₃ and NH₄HSO₃ produced by thermal reactions are oxidized to form (NH₄)₂SO₄ (fertilizer) by an electron beam. However, not all reactions were complete because the by-product contained small amounts of H₂SO₄ and NH₂SO₃NH₄ (herbicide), so a vegetable pot test was performed to study the by-product quality: no adverse effect was observed. It is inferred from the pot test that slightly acidic soil may protect vegetables from disease and a small amount of NH₂SO₃NH₄ probably affects woody species and not herbaceous species.It is concluded that the electron beam system is noted as a multi-component pollution control process (removal of NO_x, SO₃, SO₂ and dioxins) and this system will contribute to environmentally friendly use of lignite as well as agricultural productivity via fertilizer supply.     

Biotrickling filters for biogas sweetening: Oxygen transfer improvement for a reliable operation

An industrial-scale biotrickling filter for the removal of high concentrations of H₂S is described in this work. The system has been operating at H₂S inlet concentrations between 1000 and 3000 ppm_v at acidic conditions. A decrease of pH from 2.6 to 1.8 did not affect the biological activity inside the biofilter while reducing the water make-up consumption up to 75%. The current oxygen supply system, based on direct injection of air to the liquid phase, has demonstrated to be inefficient for a long-term operation leading to elemental sulfur accumulation in the packing material (i.e. promoting clogging episodes). The present study demonstrates it is possible to partially remove (40.3%) the deposited elemental sulfur by bio-oxidation when biogas is not fed. In normal operation conditions, the implementation of an aeration system based on jet-venturi devices has shown quite promising results in terms of oxygen transfer efficiency and robustness. Such improvement of oxygen transfer was translated in a better conversion of H₂S to sulfate, which increased around 17%, prolonging the lifespan operation at low-pressure drop.     

Technologies for the abatement of sulphide compounds from gaseous streams: a comparative overview

The techniques that may be applied to the removal of sulphide compounds from gases are briefly described and discussed. Scrubbing and adsorption on solids allow the recovery of sulphur either as such (H₂S or sulphide organics) or, after oxidation, as elemental sulphur or SO₂. This is actually a good choice when the concentration is high enough for sulphur recovery. When sulphur concentration is very low, techniques such as thermal and catalytic combustion, oxidative scrubbing and biofiltration might be preferable to attain deodorization. However, combustion converts sulphur into SO₂, while oxidative scrubbing gives rise to sulphate-containing solutions. Biofiltration mineralizes sulphur in a natural environmental friendly way, without producing secondary contaminants.     

Thermodynamic method for the prediction of solid CO2 formation from multicomponent mixtures

The increase in GHG concentration has a direct effect on global climate conditions. Among the possible technologies to mitigate GHG emissions, CCS is being accepted to gain emission reduction. Such technology also involves cryogenic CO₂ capture processes based on CO₂ freeze-out or where the formation of solid CO₂ must be avoided. Captured CO₂ is usually transported in pipelines for the reinjection.The risk associated to the release of CO₂ is due to the changing temperatures and pressures the system may experience, which can lead to the deposition of solid CO₂ where it must be avoided. Prolonged exposure to dry ice can cause severe skin damage and its resublimation could pose a danger of hypercapnia. It is, thus, necessary to build up a tool able to predict the conditions in which CO₂ can freeze-out.A thermodynamic methodology based on cubic EoSs has been developed which is able to predict solid–liquid–vapor equilibrium of CO₂ mixtures with n-alkanes or H₂S which are usually found in equipment for acidic gas, mainly natural gas, treatment.The focus is a detailed analysis of the method performances when more than two components are present since, for such a case, literature does not provide significant modeling results.     

Corrosion behavior of steels for CO2 injection

The process chain for Carbon Capture and Sequestration (CCS) includes tubing for injection of CO₂ into saline aquifers. The compressed CO₂ is likely to contain specific impurities; small concentrations of SO₂ and NO₂ in combination with oxygen and humidity are most harmful. In addition, CO₂ saturated brine is supposed to rise in the well when the injection process is interrupted. The material selection has to ensure that neither CO₂ nor brine or a combination of both will leak out of the inner tubing. In this comprehensive paper the investigated materials range from low-alloy steels and 13% Cr steels up to high-alloy materials. Electrochemical tests as well as long term exposure tests were performed in CO₂, in brine and combination of both; pressure was up to 100 bar, temperature up to 60 °C. Whereas the CO₂ stream itself can be handled using low alloy steels, combinations of CO₂ and brine require more resistant materials to control the strong tendency to pitting corrosion. The corrosion behavior of heat-treated steels depends on factors such as microstructure and carbon content. For different sections of the injection tube, appropriate materials should be used to guarantee safety and consider cost effectiveness.     

Thermal hazard analysis of triacetone triperoxide (TATP) by DSC and GC/MS

Thermal degradation of triacetone triperoxide (TATP) was studied using differential scanning calorimetry (DSC) and gas chromatography/mass spectrometry (GC/MS). TATP, a potential explosive material, is powerful organic peroxide (OP) that can be synthesized by available chemicals, such as acetone and hydrogen peroxide in the laboratory or industries. The thermokinetic parameters, such as exothermic onset temperature (T₀) and heat of decomposition (ΔH_d), were determined by DSC tests. The gas products from thermal degradation of TATP were identified using GC/MS technique.In this study, H₂O₂ was mixed with propanone (acetone) and H₂SO₄ catalysis that produced TATP. The T₀ of TATP was determined to be 40 °C and E_a was calculated to be 65 kJ/mol. A thermal decomposition peak of H₂O₂ was analyzed by DSC and two thermal decomposition peaks of H₂O₂/propanone were determined. Therefore, H₂O₂/propanone mixture was applied to mix acid that was discovered a thermal decomposition peak (as TATP) in this study. According to risk assessment and analysis methodologies, risk assessment of TATP for the environmental and human safety issue was evaluated as 2-level of hazard probability rating (P) and 6-level of severity of consequences ratings (S). Therefore, the result of risk assessment is 12-point and was evaluated as “Undesirable” that should be enforced the effect of control method to reduce the risk.     

Evaluating sulfuric acid reduction,substitution, and recovery to improve environmental performance and biogas productivity in rubber latex industry

Sulfuric acid is heavily used in concentrated rubber latex factories to coagulate rubber particles in skim latex. The resulting sulfate-rich wastewater creates the onset of toxic H₂S gas production in the wastewater holding ponds, causing severe corrosion to materials and community disturbance when dispersed to ambient air. This work identified and evaluated measures to reduce H₂S production by minimizing sulfate concentration in the wastewater. Sulfuric acid use could be cut down by pre-removal of ammonia in the skim latex as well as a stricter manipulation of acid dosing. In search of a more benign chemical, a heat sensitive polymer was identified and tested as sulfuric acid substitute. The use of hydroxypropyl methylcellulose polymer (HPMC) changed wastewater characteristics and was found to increase biogas production approximately by 2.4 times in batch assay at the initial pH 7.0 and methane yield by 2.7 times in continuous digester operation at HRT 7 days. Finally, a resource recovery option was evaluated. The remaining H₂S in the produced biogas was oxidized in the biotrickling filter to sulfuric acid that has a potential to partially supplement the fresh acid. This work demonstrated an integrated approach in waste management to improve environmental performance, safety and energy recovery in the concentrated latex industry.     

Enhanced NOx removal from flue gas by an integrated process of chemical absorption coupled with two-stage biological reduction using immobilized microorganisms

An integrated process of metal chelate absorption coupled with two stage bio-reduction using immobilized cultures has been proposed to continuously removal of NO_x, and the effects of SO₂, NO and O₂ concentration, gas/liquid flow rate on NO_x removal efficiency were investigated. Although nitrogen-containing components, such as Fe(II)EDTA-NO, NO₂^? and NO₃^? in the scrubbing solution, inhibited the bio-reduction of Fe(III)EDTA obviously, it was feasible to abate the inhibition effect by using the two stage bio-reduction system, and thus to improve NO_x removal efficiency. The removal efficiency decreased slowly with the increase of SO₂, O₂, NO concentration and gas flow rate, and increased with the increase of liquid flow rate. Continuously operating for 18 days, a high removal efficiency around 95% was reached by using the two-stage bio-reduction system with immobilized microorganisms, while the value decreased to 85% after 5 days of operation by using the suspended microorganisms, at a constant gas flow rate of 60 L/h containing 424–450 mg/m³ NO, 2428–2532 mg/m³ SO₂ and 3% O₂.     

Removal of H2S by co-immobilized bacteria and fungi biocatalysts in a bio-trickling filter

Biological control of odor gases has gained more attention in recent years. In this study, removal performance of a vertical bio-trickling filter inoculated with bacteria and fungi was studied. Bacteria and fungi were isolated from activated sludge in a sewage treatment plant. By adopting “three step immobilization method”, the bio-trickling filter could degrade pollutant immediately once hydrogen sulfide (H₂S) passed. The optimal empty bed resident time was 20 s. The optimal elimination capacity was about 60 g H₂S m^?3 h^?1 with removal efficiency of 95%. And the maximum elimination capacity was 170 g H₂S m^?3 h^?1. Pressure drop was ranged between 5 and 15 mm H₂O per bed over the whole operation. Removal efficiency was not affected obviously after terminating nutrient supply. The bio-trickling filter could recover back after shut down H₂S gaseous and liquid supplies simultaneously. Microbial community structure in the bio-trickling filter was not changed significantly.Combining bacteria and fungi would be a better choice for inoculation into a bio-trickling filter because of the quickly degradation of H₂S and rapid recovery under shut-down experiment. This is the first study attempting to combine bacteria and fungi for removal of H₂S in a bio-trickling filter.     

Inhibiting effects of gas–particle mixtures containing CO2, Mg(OH)2 particles,and NH4H2PO4 particles on methane explosion in a 20-L closed vessel

The main risk factors from methane explosion are the associated shock waves, flames, and harmful gases. Inert gases and inhibiting powders are commonly used to prevent and mitigate the damage caused by an explosion. In this study, three inhibitors (inert gas with 8.0 vol% CO₂, 0.25 g/L Mg(OH)₂ particles, and 0.25 g/L NH₄H₂PO₄ particles) were prepared. Their inhibiting effects on methane explosions with various concentrations of methane were tested in a nearly spherical 20-L explosion vessel. Both single-component inhibitors and gas–particle mixtures can substantially suppress methane explosions with varying degrees of success. However, various inhibitors exhibited distinct reaction mechanisms for methane gas, which indicated that their inhibiting effects for methane explosion varied. To alleviate amplitude, the ranking of single-component inhibitors for both explosion pressure (P_ex) and the rate of explosion pressure rise [(dP/dt)_ex] was as follows: CO₂, NH₄H₂PO₄ particles, and Mg(OH)₂ particles. In order of decreasing amplitude, the ranking of gas‒particle mixtures for both P_ex and (dP/dt)_ex was as follows: CO₂–NH₄H₂PO₄ mixture, CO₂‒Mg(OH)₂ mixture, and pure CO₂. Overall, the optimal suppression effect was observed in the system with the CO₂–NH₄H₂PO₄ mixture, which exhibited an eminent synergistic effect on methane explosions. The amplitudes of P_ex with methane concentrations of 7.0, 9.5, and 11.0 vol% decreased by 37.1%, 42.5%, and 98.6%, respectively, when using the CO₂–NH₄H₂PO₄ mixture. In addition, an antagonistic effect was observed with CO₂‒Mg(OH)₂ mixtures because MgO, which was generated by the thermal decomposition of Mg(OH)₂, can chemically react with water vapor and CO₂ to produce basic magnesium carbonate (xMgCO₃·yMg(OH)₂·zH₂O), thereby reducing the CO₂ concentration in a reaction system. This research revealed the inhibiting effects of gas‒particle mixtures (including CO₂, Mg(OH)₂ particles, and NH₄H₂PO₄ particles) on methane explosions and provided primary experimental data.     

Preoptimal analysis of phase characteristic indicators in the entire process of coal spontaneous combustion

To accurately predict the development degree of coal spontaneous combustion (CSC), the CSC process was investigated using a programmed high-temperature-heating experimental system, and the variation law of index gas concentration in the holistic process of CSC and oxidation is formulated. Additionally, the accuracy of the experimental system was evaluated using experimental design for thermal analysis, and the correlation between gas index and apparent activation energy was determined using grey correlation analysis. The results indicated the following. In the critical temperature stage (0–100 °C), φ(CO)/φ(CO₂) should serve as the main index and C₂H₄ should serve as the auxiliary index; in the crack-active-speedup temperature stage (100–260 °C), CO and φ(C₂H₄)/φ(C₂H₆) should serve as the main index and R₁, the Graham index, and φ(C₂H₄)/φ(CH₄) should serve as auxiliary indexes; in the speedup-ignition temperature stage (260–370 °C), R₂ and the Graham index should serve as main indexes and φ(CO)/φ(CO₂), C₂H₄, and R₁ should serve as auxiliary indexes; in the ignition temperature (370–500 °C), R₃ should serve as the main index and R₂, the Graham index and C₂H₄ should serve as auxiliary indexes. Among them, the grey correlation degrees among the Graham index, Grignard fire coefficient, and apparent activation energy were the highest, reaching 0.91.     

Hydrogen explosion incident mitigation in steam reforming units through enhanced inspection and forecasting corrosion tools implementation

Hydrogen (H₂) explosion effects recently examined, are confirming the devastating loss scenarios to humans, environment, assets, and associated business interruption. H₂ production is a core process in refineries used in further process steps. Steam reforming of natural gas or a mix with naphtha or LPG is a common hydrogen production technique, where the latest technologies have adopted enhanced metallurgies to minimize explosion risk and the associated maintenance cost following plant degradation owing to corrosion effects. However, corrosion rates are still high in specific areas of piping and process equipment. The aim of this paper is to present a methodology based on semi-quantitative RBI modeling according to regulations by API and recent EN standards, adopting a family of linear regression forecasting models that depict the yearly corrosion rate (per corrosion loop) of a hydrogen production steam reforming unit; this is done under different operating conditions (e.g., temperature, pressure, and fluid speed), metallurgy and other related physicochemical variables. The model is based on the examination of both ultrasonic wall thinning measurements and the examination of quantitative crosslinking total corrosion effects along with the physicochemical properties prevailing in different plant corrosion loops. The outcome of the regression analysis is an expansive family of multivariable equations describing, with a defined accuracy, the yearly corrosion rate and associated lifespan forecast per corrosion loop, and per examined part. These equations were further utilized in a custom-made database that can be used as an additional loss prevention tool by the hydrogen production unit management team. Evaluation results regarding the tool efficiency are presented in the following of this paper.     

A method of analysis for gas explosions: H2Se case study

This paper presents a methodology for conducting a simplified gas-explosion analysis when there are uncertainties about the amount of fuel involved and the mode of combustion. The methodology is illustrated by a case study of an explosion of a cloud of hydrogen-selenide (H₂Se), nitrogen and air. Hydrogen-selenide (H₂Se) diluted with N₂ is used in a reactor vessel to produce solar cells. An explosive mixture could be created if the reactor vessel failed and its contents mix with ambient air. Mixtures of 20% or 6% H₂Se in N₂ were considered as feedstock into the reactor. It was determined theoretically that an explosion involving either mixture would challenge the reactor room's integrity. However, it is unlikely that a local ignition will propagate in the dilute 6% H₂Se mixture, because its adiabatic flame temperature is only 850 K; the 20% mixture is borderline flammable. Because of the proximity of personnel to the reactor room and the high toxicity of H₂Se, any damage to the room boundary is considered unacceptable. To prevent accidental mixing of H₂Se with air in the reactor, a nitrogen buffer was installed between the reactor vessel and the ambient air.     

水平弯管内硫沉积数值模拟研究

元素硫在集输管道中沉积会引起堵塞和腐蚀问题,而弯管是集输管道中较易出现硫沉积的部位之一。为此,采用数值模拟的方法研究水平弯管内的硫沉积问题,首先利用雷诺应力模型对流场进行模拟,其次采用Lagrange颗粒轨道模型对硫颗粒进行模拟追踪,研究不同因素对硫颗粒在弯管中沉积率的影响。结果表明:弯管内壁会出现负压区和低速区,气流速度和弯曲比会对流场产生影响;硫颗粒在弯管中的沉积率随流速、粒径和弯曲比的增大而增大;硫颗粒沉积是重力和离心力共同作用的结果,其中离心力是导致弯管中沉积率增大的重要原因。     

Hydrogen sulphide removal from landfill gas

Control of odours should be considered to be a fundamental issue in order to site, design and manage sanitary landfills. With regard to construction and demolition (C&;D) debris, landfilling was the mainly adopted solution in many European Countries; in particular, gypsum drywalls can produce high concentrations of hydrogen sulphide (H₂S) in landfill gas ranging from 7 ppm to 100 ppm. In some cases also dangerous concentrations until to 12,000 ppm were detected. In this paper H₂S removal efficiency in a lab-scale vertical packed scrubber was investigated. Hydrogen sulphide abatement was evaluated for inlet H₂S concentrations of 1000–100–10 ppm, adjusting scrubbing liquid pH in the range 9–12.5 by means of caustic soda (NaOH 2N solution). Moreover, best operating conditions for the system were defined as well as H₂S abatement along the tower and liquid recirculation effectiveness in case of inlet H₂S concentration of 10 ppm (typical odour concentration). Results showed that pH of 11.5 in scrubbing liquid could be considered the best value for removal of different inlet H₂S concentrations, also taking into account parasitical consumption of NaOH due to CO₂ absorption. Moreover, in case of continuous working of the system at H₂S concentration of 10 ppm, strong removal efficiency was already obtained with a packed bed height of about 70 cm. Significant performances were ensured after 1 h of constant activity, consuming about 3 ml of soda per cubic meter of polluted air. Subsequently liquid blowdown was necessary.     

Feasibility study of decomposing methane with hydroxyl radicals

Coal-mine gas disaster is one of the most serious coal-mine disasters in China. The main component of coal-mine gas, methane is chemically stable and very difficult to be degraded by conventional methods. Hydroxyl radical (OH), due to strong oxidizing ability and high electro-negativity, is the primary degradation source of atmospheric methane. In the present study, methane degradation using hydroxyl radicals generated by Fenton’s reagent, Fe²⁺/H₂O₂, has been carried out in the self-designed bubbling reactor. The effects of H₂O₂ concentration, dosage of FeSO₄·7H₂O and initial pH value on methane removal efficiency were investigated respectively. It has been found that the optimal reaction conditions were 100 mM of hydrogen peroxide, 2.00 mM of ferrous ion and initial pH value of 2.5. Under optimal conditions, the removal efficiency of methane reached 25% after 30 min. The preliminary experimental results unambiguously demonstrate that the degradation of methane using hydroxyl radicals generated by Fenton’s reagent is feasible.