Liquefaction of coal by SRC‐II process: Part I: A new kinetic model

Abstract

The kinetic experiments were carried out in a continuous stirred tank reactor. Practically important ranges of SRC‐II reactor temperature (444–466°C), pressure (10.4–20.8 MPa), nominal slurry residence time (0.54–1.62 h), coal concentration in the feed slurry (25–35 wt%), and inorganic mineral matter concentration (4.75–13.43 wt%) were covered in a total of 43 experimental runs. In each of the experimental runs, the feed slurry was formulated by using vacuum tower bottoms from SRC‐II pilot plants using the same feed coal (Powhatan No. 5), to obtain feed compositions similar to those obtained in SRC‐II pilot‐plant recycle operation. The kinetic model considers the overall conversion to be achieved in two stages. The first stage is the instantaneous dissolution of coal and in the rate controlled second stage all the reactive organic components in the liquid phase are initially assumed to react, each yielding components lighter than itself. The distribution of products in each reaction stage is considered to be independent of the operating conditions. The best rate controlled (second stage) reaction scheme and values of the unknown parameters are obtained by minimizing the overall difference (i.e. for all the components over all the runs) between the measured and model predicted mass fractions of the various components in the reactor. This analysis identifies the reaction of solvent refined coal (pyridine soluble organic matter boiling above 482°C) to be the only significant reaction in the second stage and its rate is determined to be ‐rSRC = 1.567 × 105 exp (‐79.16/RT) · p0.28 H 2 · XASH, kg/L h. Overall error in this analysis yielding the reaction scheme, rSRC and values of product distribution coefficients for both the reaction stages is less than 8% absolute i.e. ±4%.

Some Aspects of Design of Commercial Reactors for Direct Coal Liquefaction

“…The left hand side of above equation -the heat removal term consisting of convective gas and liquid phase flow, in addition, heat removal by quench flow-can be expressed as QR = pLCn + g(l + q)PGCPGT _ (PLCn + gpGCPG)1;, + gqpGCPGT" (12) 'L 'L where: (13) It can be easily seen that the heat removal rate QR is a linear function of temperature T (14) where: fJ = (PLCn + gpGCpdTo + gqpGCPGT" (15) 'L are assumed to be constant for the reaction system. …”

Liquefaction of coal by SRC‐II process: Part IV: Steady‐state thermal behavior of the reactor

“…v' 'I 1 ues of the distribution coefficients are available in reference (Singh et al, 1982a). It is to be noted thatfir' andf'yr', i.e., distribution coefficients for hydrogen reaction during instantaneous coal dissolution and rate-controlled SRC reaction, both have negative values.…”

Liquefaction of coal by SRC‐II process: Part II: Simulation of an SRC‐II recycle system

“…and fsR' , for i = 1,. .. 10) for Powhatan coal are available in Table 4 of Singh et al (1982). The method to obtain distribution coefficients for a different coal is described later in the text.…”

“…However, these correlation models do not provide any significant insight of the process, and their applicability is also very limited. The new kinetic model (Singh et al, 1982) provides a very good basis for understanding the SRC-I1 process from a fundamental point of view. It is expected that the analysis of the behavior of SRC-I1 reactors with recycle, based on this kinetic model, would provide some meaningful insight of the process.…”

“…It is expected that the analysis of the behavior of SRC-I1 reactors with recycle, based on this kinetic model, would provide some meaningful insight of the process. The available kinetic model (Singh et al, 1982), idealized hydrodynamic and thermal conditions in the reactor (isothermal CSTR), and an idealized scheme for the separation of various components in the product stream are used in the development of *Department of Chemical and Petroleum Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania 1526 1. the present recycle model. "Degrees of freedom" concept has been used to evaluate the number of process variables that can independently be fixed to define all the conditions throughout the recycle system.…”