Material and Energy Balances Report

A guide to the preparation of process material and energy balance reports for systems is given. Such reports effectively summarize and current available information/data for the process.

Introduction

Summary

Flow Diagram Basis

State design premises including on-stream time efficiency, production rates, flexibility, yields, conversions, by-products, and unaccounted-for-losses.

Production Rates

The annual rate of production should be stated in units commonly used for the product. This figure should agree with that used in the project scope. The product quality should be clearly defined, e.g., "dry or wet basis," "refined," etc.

Operating Factors

The annual operating hours, ratio of maximum to average flows, etc., should be recorded. These critical items must be determined carefully. The factors which combine to make up these items should be explained in detail in the supporting calculations. This allows the design engineer to provide adequately for operating requirements without compounding safety factors.

Operating Units

When a fixed number of parallel operating units or systems is required because of specified equipment capacities or known limitations, the reasons should be given.

Basic Parameters

The basic parameters used in preparing the material and energy balances should be documented (base temperature for enthalpy, heating values for feedstocks and products, the electric power basis, stack gas losses, evaporation losses, etc.).

Other Factors

Almost every flow diagram includes some assumption in addition to the foregoing. For example, a purchased crude material may contain a variable amount of impurity, whose removal requires distillation facilities and related utilities. If the material and energy balance is based upon the maximum percentage of such impurity, this qualification should be stated.

Engineering Assumptions

For processes that are in the bench to pilot plant scale of development, a great number of processing and equipment performance assumptions will necessarily be used. Some assumptions are easily obtained from similar unit operations of commercial processes. Other assumptions must be regarded as speculative and subject to engineering judgments. All assumptions and design practices should be fully documented. This will allow an assessment of their impact on the overall economics.

Material and Energy Balance

Include a material and energy balance flow diagram of the process. Also, include process balance stream lists which give the material and energy balances.

Process Stream Tables

Provide a tabulated material and energy balance (keyed to the process flow diagram) in sufficient detail for the purpose of the report. The minimum information includes the flow rates and compositions of the feed and of the products. The flow rates and composition of intermediate streams should be shown when the information is needed by those who are to use the report.

Utilities Requirements

Describe the utility requirements as set forth by the utility requirements forms. Include utility flow diagrams.

Waste Steams and Emissions

Describe the waste and emission steams. Apparently inconsequential side streams, such as drain lines, waste streams, rejected charges, and spills should not be neglected.

Material and Energy Balance Flow Diagrams

Include Material and Energy Balance block flow diagrams. Often material and energy balance tables are included on material and energy balance flow diagrams for convenience.

Overall Balance

An overall process stream material and energy balance flow diagram for the entire plant should be included. Separate overall utility material and energy balance flow diagrams should also be prepared for the plant water and steam systems.

Individual Processes

Material and energy balance flow diagrams should be prepared for each of the individual processing steps. Consideration should be given to developing separate material and energy balance flow diagrams for nitrogen, oxygen, and sulfur balances.

Discussion

Complicated qualifications should be expanded in a process description and the supporting calculations. A discussion of how rigorous or how inflexible each assumption might be and which factors are limiting permits the design engineer to take advantage of research and operating know-how.

Appendices

Supporting Calculations

Calculations are included to clarify the basis of the numbers developed for the material and energy balances. Generally, only those calculations need be included which involve assumptions or which cannot be readily reproduced by an experienced engineer. Thus, routine calculations may be omitted. Much of the information summarized on flow diagrams is developed from detailed calculations based on available data, and, at times, significant assumptions. Such calculations should be included. Where repetitive or voluminous calculations are involved, samples will suffice. It is important to include all those calculations which are based on assumptions or which cannot be readily produced by an experienced engineer.

Physical/Chemical Properties

Include physical and chemical property data as needed to substantiate material and energy balances.

Where basic design data for process are not presented by means of a flow diagram, such information may be shown by calculations and tabulations. These property estimation calculations need not go beyond those made in testing experimental data and in organizing the report.