Nitrogen content coal liquids

Solid fuels, unlike gases and liquids, are entirely characterized by their composition. For example, coal can be characterized by its carbon, hydrogen, oxygen, sulfur, and nitrogen content. The water and mineral content of coal are also important means of differentiating coals from various sources. 

Shale oils are dark-brown, viscous, waxy liquids that usually contain higher concentrations of nitrogen and oxygen heteroatoms than coal liquids or crude oil. Oils can often have high pour point temperatures and may have trace concentrations of arsenic. Nitrogen levels of 2% and oxygen concentrations of 1.5% are typical. The sulfur content averages about 1%. 

Properties. Pilot-unit data indicate the EDS process may accommodate a wide variety of coal types. Overall process yields from bituminous, subbituminous, and lignite coals, which include liquids from both liquefaction and Flexicoking, are shown in Figure 14. The liquids produced have higher nitrogen contents than are found in similar petroleum fractions. Sulfur contents reflect the sulfur levels of the starting coals ca 4.0 wt % sulfur in the dry bituminous coal 0.5 wt % in the subbituminous and 1.2 wt % sulfur in the dry lignite. 

Typically, liquids derived from coal are lower in hydrogen content and contain more impurities than do petroleum products. These impurities consist of atoms other than hydrogen and carbon, that is, nitrogen, sulfur, oxygen, and inorganic materials. Upgrading of coal liquids to make specification fuels typically involves both hydrogen addition and removal of impurities. 

The asphaltene content correlated with the nitrogen content of the liquids, thus supporting the use of nitrogen content to monitor the extent of coal-liquid upgrading. 

Table III lists the specific gravity, nitrogen content, and sulfur content of the various distillation fractions obtained from each of the eight coal liquids. Nitrogen content increased for the higher-boiling distillates as expected. All sulfur values were low as expected. Nitrogen contents of the asphaltenes from the bituminous-coal liquids were higher than those from the lower-rank-coal liquids.

Linear regression results for the correlation of the PAP contents of the 200° to 325° C, 325° to 425° C, and 425° to 540° C distillates with the distillate nitrogen content gave correlation coefficients of 0.85, 0.96, and 0.93, respectively, indicating very good correlations. Data for the middle distillate are plotted in Figure 4. Thus, the trend in PAP content may very well be more dependent on nitrogen content than on coal rank for these liquids. 

Table III shows elemental composition of typical sour petroleum, coal syncrudes or shale oils. Compared with typical sour petroleum, the coal syncrude is lower in sulfur content but significantly higher in nitrogen. Compared with shale oil, coal syncrude is lower boiling and contains only about one half the nitrogen. A major difference between the two liquids is the highly aromatic structure of coal liquids and the absence of long paraffinic structures. Shale oil is more aromatic than petroleum but significantly less aromatic than coal liquids. This is mirrored by the hydrogen contents which were shown in Table I.

Coal liquids require less severe hydrotreatments than shale oil due to the lower nitrogen content. 

This was anticipated since the relative nitrogen content of the coal derived liquids 1s higher than either baseline fuel (0.44% versus 0.29% typically). However, the combination of burners out of service and low excess air reduced N0X emissions from the coal derived liquid as much as 50% in some cases (Figures 4 and 5). Table II lists some typical N0X reduction results for the Intensive test matrix. 

However, coal derived liquids which have been severely hydrotreated to achieve nitrogen contents of less than 0.1 wt % are estimated to represent about the same cost as methanol. 

The major question involving burning characteristics of coal liquids relates to the higher nitrogen content compared to petroleum fuel oils and the potential effect on NO emissions. Since NO emissions are sensitive to burning conditions, however, actual burning tests are required under various conditions to assess the effects. 

Enthalpy of Formation and Absolute Entropy of Coal Liquids. Coal-derived liquids are of extremely complex compositions including highly aromatic groups. They are also characterized by their high contents of heteroatoms, such as oxygen, nitrogen and sulfur. 

Coal Liquids and Shale Oil. Some properties of five coal liquids and a hydrotreated shale oil are given in Table I, including sulfur, nitrogen, acid and base contents, and distributions by boiling range. Ring-number... 

In all of these experiments conversions of coal to liquid products were 90 =b 3 wt %, recoveries of gases, liquids, and solids were greater than 93 wt % of the materials charged, and conversions of coal to 1016° F— distillable products were greater than 80 wt %. Distillation data and nitrogen content of distillate and residual fractions of the filtered liquid products from a number of experiments in Table V are presented in Table VI. 

In other fuel markets, coal liquids can be more competitive. Industrial boilers presently are not amenable to stack gas scrubbing. The same is true of smaller utility plants. In particular, peak load units require a clean, storable liquid fuel as an alternative to natural gas. However, the high viscosity of primary coal liquefaction products is undesirable for many of these applications. Also, their residual sulfur and nitrogen contents may be excessive as emission standards become more stringent. 

Primary coal liquids must be upgraded in order to serve these markets. A logical route is to use current black oil conversion technology as practiced in the petroleum industry (2). An applicable UOP process is RCD Unibon (3). This comprises the direct processing of petroleum residues to reduce the sulfur and nitrogen content of heavy fuel oil or to combine desulfurization with conversion of residue to lighter, more valuable products. 

This chapter reports results of applying a catalytic hydrorefining process to four coal liquids solvent-refined coal (SRC) process filter feed, SRC extract product, Synthoil, and H-Coal process hydroclone underflow. The achieved upgrading is evaluated in terms of reduction in benzene and heptane insolubles, reduction in sulfur, nitrogen, and oxygen, an increase in hydrogen content, and a yield of lower boiling products. 

Several processes have been developed for coal liquefaction. Large-scale pilot plants have been in operation for the solvent-refining coal (SRC) process, and a pilot plant is being constructed for the H-Coal process, which is a direct catalytic process. Construction of demonstration plants is under consideration. The coal liquids produced from the current processes contain large amounts of residual fuels. They probably will be used initially as boiler fuels for stationary power plants. However, the nitrogen content of coal liquids is much higher than the petroleum residual fuels. The sulfur contents of coal liquids can vary considerably they depend on the type of coal and the liquefaction process used. Current coal liquefaction processes are capable of produc-... 

Some coal liquefaction methods, such as the Synthoil (5) process and the CO-steam (6) process, are similar to solvent refining in their approach, but more severe conditions or a catalyst are used to give a fiuid product. In the Synthoil reaction, bituminous coal is pulverized, dispersed in a vehicle oil, and hydrogenated in a packed tubular reactor with or without added catalyst. The CO-steam process uses lignite coal and less expensive synthesis gas. The intended product is a heavy liquid fuel having ash, sulfur, and nitrogen contents suflBciently low to avoid stack-gas cleaning. Reactor temperature and pressure are normally 400°-450°C and 4000 psi, respectively. 

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