4 May, 2015
Benefits of Standby Time in Adsorption Dehydration Process
Molecular sieves are used upstream of turboexpander units and LNG facilities to dehydrate natural gas to <0.1 ppmv. In the natural gas industry, the molecular sieves employ heat to drive off the adsorbed water. The cyclical heating/cooling of the adsorbent results in a capacity decline due to a gradual loss of crystalline structure and/or pore closure. A more troublesome cause of capacity decline is contamination of the molecular sieves due to liquid carryover from the upstream separation equipment. Because of the capacity decline curves flatten out, available standby time may be able to extend the life of a molecular sieve unit when your unit is operating on fixed cycle times. Other operating options include: running each cycle to water breakthrough; and, reducing the cycle times in discreet steps throughout the life of the adsorbent. To illustrate the benefits of standby time, a case study was evaluated and the results are presented.
Read More >10 Apr, 2015
Estimating Sour Gas Water Content by New Correlations and Simplified Charts
In April's "Tip of the Month," we will present a set of correlations and simplified charts for estimating sour gas water content directly without having to look up the water content of sweet gas. These correlations are based on the Wichert and Wichert chart (Figure 20-9 of the GPSA data book) and Wagner and Pruss water vapor equation and Bukacek correlation for estimating sweet gas water content. The proposed correlations are valid for pressures up to 24 MPa (3500 psia), temperatures up to 175°C (350°F) and H2S equivalent concentrations of up to 50 mole %. The accuracy of the proposed correlations was compared against limited experimental data and a rigorous method using an equation of state.
Read More >3 Mar, 2015
Process Safety and Low Oil Prices
In this edition of our Tip of the Month series, we reflect back to December 2008, and get a reminder from the United States Chemical Safety Board (CSB) to remain focused on process safety and accident prevention during this time of lower oil prices. During the economic downturn of 2008, oil prices dropped significantly. The latest drop in crude oil prices is similar. At that time, the CSB produced a video message asking companies to stay focused on process safety. That message is still very relevant today.
Read More >12 Feb, 2015
Why CO2 Flashing from Water is Important for CO2 EOR Flood Separators and Tanks
In this Tip of the Month (TOTM) we will discuss how to determine CO2 solubility and flashing issues in water at pressures and temperatures commonly associated with gathering systems and production facilities. This is mainly important for CO2 Enhanced Oil Recovery (EOR) floods as the CO2 concentration is high and the initial separation is at higher pressures than is common in non-CO2 EOR oilfields. These two conditions result in significant dissolving of CO2 into the produced water with resultant flash gas from downstream Free Water Knockouts (FWKO), treaters, and tanks. In mature CO2 EOR floods with Water-Alternating-Gas (WAG) injection schemes, it is likely that most of the flash gas in the downstream separations will be from the produced water. While this TOTM is significant mainly for CO2 EOR floods, the following analysis is general in nature; it would apply to other situations involving CO2 solubility in water issues. This analysis assumes that there is no H2S. H2S would have somewhat higher solubility than CO2 which would force more gas to flash from the FWKO and tanks. Higher H2S than about 5% would begin to appreciably increase the solubility of H2S into water.
Read More >21 Jan, 2015
Variation of Crude Oil Properties with Temperature in a Gathering Line
In the October and November 2014 Tips of the Month (TOTM), we demonstrated that Gas-Oil-Ratio (GOR) has a large impact on the capacity of crude oil gathering lines. If GOR is less than the saturation solution gas, the increase in GOR reduces the viscosity and density of crude oil which causes the pressure drop to decrease. However, if the GOR exceeds the saturation solution gas the system becomes two phase and pressure drop increases. The solution gas is a function of temperature, pressure, gas and liquid compositions. In this TOTM, we will study the impact of temperature on the crude oil properties in the gathering systems for the case presented in the November 2014 TOTM. Specifically, the variation of the crude oil relative density and viscosity with the temperature will be studied. Finally, the impact of temperature on the oil and gas velocity and pressure drop along a gathering line for nominal pressure of 6900 kPag (1000 psig) and nominal pipe size of 101.6 mm (4 inches) will be demonstrated using a multiphase rigorous method from a commercial simulator. The calculated properties, oil and gas velocities and pressure drops are presented in graphical format as a function of the oil stock tank volume flow rate, solution gas, Rs, and temperature.
Read More >7 Oct, 2014
Impact of Gas-Oil Ratio (GOR) on Crude Oil Pressure Drop in Gathering Systems
In the June 2008 Tip of the Month (TOTM), we demonstrated how general-purpose process simulation programs can be used to simulate gas dominated two-phase pipelines. In the August 2008 TOTM, we discussed the value of the simple Flanigan correlation and how it can be used to model and analyze the behavior of a wet gas transmission pipeline. The results of the Flanigan correlation were compared with more rigorous calculation methods for multiphase pipelines. In this TOTM, we will study the impact of gas-oil ratio (GOR) on pressure drop in crude oil gathering systems. Specifically, pressure drop along a gathering line for nominal pressures of 690, 3450, and 6900 kPag (100, 500, and 1000 psig) and nominal pipe size of 101.6 and 152.4 mm (4 and 6 inches) was calculated using multiphase rigorous method from commercial simulator. The calculated pressure drops are presented in graphical format as a function of the oil stock tank volume flow rate and GOR. Variation of thermophysical properties was considered.
Read More >3 Sep, 2014
Lean Sweet Natural Gas Water Content Correlation
In the October, November, December 2007 and February 2014 Tips of the Month (TOTM), we studied in detail the water phase behaviors of sweet and sour natural gases and acid gas systems. We also evaluated the accuracy of different methods for estimating the water content of sour natural gas and acid gas systems. The water vapor content of natural gases in equilibrium with water is commonly estimated from Figure 6.1 of Campbell book or Figure 20.4 of Gas Processors and Suppliers Association (GPSA), including corrections for the molecular weight (relative density) of gas and salinity of water. In this article, we will present two new correlations for estimating the water content of lean and sweet natural gases. The performance of the proposed correlations is compared with the rigorous simulation and shortcut method software and other correlations.
Read More >4 Aug, 2014
The Importance of Leadership in Process Safety Management
The first pillar of Risk Based Process Safety Management is “Commitment to Process Safety.” A formalized mentoring system can ensure workforce involvement, compliance with company and regulatory requirements, increase the competency of personnel and enhance the process safety culture of the entire organization. Within this element there are several essential features that lead to a more effective process safety culture. Providing strong leadership is critical for any organization that strives to manage the risk associated with the activities associated with process safety. Leadership is a skill that is not necessarily intuitive to managers and mentors. Leadership is a skill that can be learned. In this Tip of the Month (TOTM), we explore process safety leadership.
Read More >11 Jul, 2014
Gas Sweetening-Part 1: Comparison of Amines
Several alkanolamines have been used for acid gas removal from natural gas streams. In this study only a primary monoethanolamine (MEA), a secondary diethanolamine (DEA) and a tertiary methydeithanolamine (MDEA) are considered. MEA has the highest reactivity and MDEA has the highest selectivity. In this TOTM, we will study and compare the performance of these three amines by simulation of a simplified process flow diagram for removal of H2S and CO2 from a sour gas stream. The H2S and CO2 concentration in the sweet gas, amine solution circulation rate, reboiler duty, amine losses, pump power, and lean-rich heat exchanger (HEX) duty are calculated and plotted for a wide range of steam rates needed to regenerate the rich solution. In addition, the optimized steam rate and corresponding design variables are determined and reported.
Read More >22 Apr, 2014
Simple Equations to Approximate Changes to the Properties of Crude Oil with Changing Temperature
This article describes simple equations to approximate changes to the properties of crude oil with changing temperature. Changes in crude oil density and specific heat, or heat capacity, can be estimated from graphs and/or more elaborate computer simulation. The latter generally requires access to a process simulator and characterization data for the crude oil. A suitable, tuned computer model is likely the most accurate method of estimating the fluid properties, but is not always available. Direct laboratory measurement is also possible if facilities and oil samples are available and a high degree of accuracy is required.
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