B-1). The basic nitrogen compounds, which are composed mainly of pyridine-type homologs and occur throughout the boiling ranges of organic compounds, which are usually of the pyrrole, indole, and carbazole types, have a decided tendency to exist in the higher boiling fractions and crude oil residua and in liquids from alternative energy sources such as biomass and organic waste.
Organic nitrogen-containing compounds have many important roles in nature (hence, also in biomass) and display an enormous structural diversity, in which the nitrogen atoms can form part of simple functional groups or complex heterocyclic systems. The basic nitrogen compounds also have varying degrees of substitution and oxidation. The most noteworthy of these naturally occurring molecules are proteins, and most vitamins and hormones. Furthermore, nitrogen compounds in liquids produced from a variety of sources (including biomass and organic waste) can have a deleterious effect on any catalysts used to upgrade the liquid.
Basic nitrogen compounds with a relatively low molecular weight can be extracted with dilute mineral acids; equally strong bases of higher molecular weight remain unextracted because of unfavorable partitioning between the oil and aqueous phases. A method has been developed in which the nitrogen compounds are classified as basic or non-basic, depending on whether they can be titrated with perchloric acid in a 50:50 solution of glacial acetic acid and benzene.
Table B-1 Non-basic and basic nitrogen types.
Nitrogen compounds extractable with dilute mineral acids from renewable fuels typically consist of alkyl pyridine derivatives, alkyl quinoline derivatives, and alkyl isoquinoline derivatives carrying alkyl substituents, as well as pyridine derivatives in which the substituent was a cyclopentyl or cyclohexyl group. The compounds that cannot be extracted with dilute mineral acids contain the greater part of the nitrogen in crude oil and are generally of the carbazole, indole, and pyrrole types.
Thus, the presence of the various types of nitrogen compounds in any feedstock must be monitored because they can critically affect aquatic ecosystems, especially their high levels can cause eutrophication under certain conditions. Ammonia, organic species, nitrate derivatives (-NO3), and nitrite derivatives (-NO2) can be present in wastewaters. In general, ammonia and organic species are the most common in raw water. Ammonia is the initial product of the decay of nitrogenous organic wastes, its presence being an indication of such wastes. Typically, the nitrate content in waters is low but can rise to appreciable levels in wastewater from agricultural activities as a result of soil fertilization. Also, nitrite derivatives are present in low concentration since these are rapidly oxidized to nitrates, while nitrite derivatives can be found in wastewaters from the microbiological reduction of nitrate or the oxidation of ammonia.
See also: Waste, Waste Disposal.
Basic Sediment and Water
The basic sediment and water (often referred to in a shortened form, such as BS&W, BSW) is the material which collects in the bottom of storage tanks and is usually composed of oil, water, and foreign matter, also called bottoms or bottom settlings. The material is also known as bottoms, bottom sediment, bottom settlings, sediment, and water.
The particulate matter is known as sediment or mud. The water content can vary greatly from fuel to fuel (conventional or alternate). The bulk of the water and sediment is usually separated as soon as possible after production to minimize the quantity that needs to be transported and/or transferred to subsequent processing units. Further, the residual content of these unwanted impurities is measured as bottom sediment and water (BS&W, ASTM D4007).
Thus, basic sediment and water are both a technical specification of certain impurities in any fuel and the method for measuring it. In many raw fuels (including fuels produced from biomass), the crude oil will contain some amount of water and suspended solid from the starting material. The particulate matter and the water content can vary greatly from feedstock to feedstock and from process to process. The bulk of the water and sediment is usually separated at the earliest possible convenience to minimize the quantity that needs to be transported further as well as any adverse effects on the process and process equipment.
Upon production of a fuel from a renewable source, the fuel typically passes through facilities that allow gas and water to separate from the crude and solids to settle out. These facilities may comprise a simple gathering tank or a series of specialized separation vessels, and may involve the addition of chemicals to the crude to aid in the separation of various contaminants from the crude oil and natural gas.
The BS&W test has been used to determine composition of the fuel from many sources and should be tested frequently to ensure it meets the prescribed quality requirements. There are two tests conducted, a bottom sediment and water test (BS&W) and a visual test. The BS&W test is done at the beginning, mid-point, and end of the fuel production train. Visual tests are conducted every fifteen minutes during the evolution. The visual criteria is simply that the fuel be clear and bright and the test is a quick and easy check of the fuel quality.
See also: Refining.
Batch-Type Processes
A batch process is usually performed over and over, and batch processes are a sub-class of sequential processes. Batch process refers to a process that involves a sequence of steps followed in a specific order. Also, batch processes generate a product but the sequential processes need not necessarily generate a product. Thus, batch processing is a technique for automating and processing multiple portions of a feedstock More generally, industrial processes can be divided into two categories of production which are (i) continuous processes and (ii) batch processes.
Continuous processes are designed to run at steady state, and to maximize the efficiency of these processes, it is necessary to keep the plant in the operating range under disturbances. The optimization task required to operate such processes is usually performed to achieve disturbance rejection, designing controllers to reach and maintain set-point effectively, and keeping the down time to a minimum. Since the operating range is generally very narrow, the system dynamics can often be approximated by linear dynamics.
Batch processes have a finite operating time, rather than a continuous operation. The control objective in batch processing is not to reach steady state, but to reach some desired objective by the end of the batch. This can involve movement through a very wide operating range, and non-linearity in the system can be strong. Batch optimization focuses on maximizing the performance objective by finding the corresponding input variable and state variable trajectories. Since batch production is usually of low volume, high value production, optimization of its operation is critical to make the process viable.
The most common type of process for acid gas removal is the batch-type process, and many involve a chemical process in which the acid gas reacts chemically with the cleaning agent, usually a metal oxide. These processes are not merely physical separation processes in which the acid gas is removed by a physical phenomenon, such as adsorption. Thus, the batch-type processes have the common requirement that the process be operated as a batch system where, at the end of the cycle, the chemical agent must be changed or regenerated in order to continue treating.
Batch processes are limited to removing small amounts of sulfur from fuels, especially when the flow rates of the gas streams and/or there are small concentrations of hydrogen sulfide. These processes include (i) the iron sponge process, (ii) the ChemSweet process, (iii) the SulphaCheck process, (iv) the SulphaTreat process, (v) the zinc oxide process, and (vi) the
