CHE 4173 Water Integration Assignment 2020 | SEMESTER 1 MARKS: XXXXXXXXXX% of your total mark) PART A Data Extraction and Water Reuse/Recycle (20 MARKS) Question A1 (5 marks) Extract the water...

CHE 4173 Water Integration Assignment

2020 | SEMESTER 1

MARKS: 100 (20% of your total mark)

PART A
Data Extraction and Water Reuse/Recycle (20 MARKS)

Question A1
(5 marks)

Extract the water limiting data for water recovery in the Pulp mill as shown in Figure A. Note that water is loss from pulp washing and chemical recovery while water is gain at direct contact condenser. Several wastewater streams (water gains) are the potential water sources to be recovered in the pulping process. Steam will not be considered as part of the water limiting data as the boiler feed water has other contaminant constraint e.g. salt.

The following constraints on feed flowrate and methanol concentration should be satisfied for the water demand while considering water recovery:

i. Counter-current multistage washing:

Flowrate of wash water = 467 ton/h

Methanol concentration in wash water ≤ 20 ppm

ii. Chemical recovery

165 ≤ Flowrate of feed water (ton/h) ≤ 180

Methanol concentration in feed water ≤ 20 ppm

iii. Direct contact condenser

Flowrate of feed water = 8.2 ton/h

Methanol concentration in feed water ≤ 10 ppm

Question A1 will due by 5^th
May, 23:59. After submitting your answer to moodle submission link you will be given the correct limiting data to complete the rest of the assignment.

Question A2

For the limiting water data identified in Question A1, determine the minimum fresh water and wastewater flowrate targets and the pinch concentration using either one of these two different targeting methods - composite curve and water cascade table. Assuming town water source is available at 0 ppm methanol. Calculate the amount of town water saved (15 marks)

Figure 1
A Kraft pulping process (basis: 1 hour; T refer to ton/h; values in parenthesis indicate methanol concentration in ppm)

PART B
Water Network Design (30 MARKS)

Question B4

(a) Design a water network using grid diagram or NNA to achieve the water targets in Question A2, considering town water source at 0 ppm. You should use the limiting flowrate in your design (10 marks)

(b) Identify the wastewater streams generated from the water network and tabulate their flowrates and concentration in a table (4 marks)

Question B5

Given the water network you have designed in Question B4, you are required to remove methanol contaminant from wastewater using a methanol treatment process. Assuming the oil extraction process is capable of treating the methanol to an outlet concentration of C_out
= 60 ppm. Given the discharge limit for methanol concentration is C_D
=
100 ppm

(a) Target the minimum effluent treatment flowrate using effluent composite curve (3 marks)

(b) Design a distributed methanol treatment system using the pinch design rule (3 marks)

(c) A recent more stringent regulation requires the effluent to be treated to C_D
=
80 ppm
before discharge to the environment. Few options could be considered to meet the new discharge limit

(i) Calculate the new wastewater treatment flowrate (3 marks)

(ii) Methanol extraction efficiency can be increased without changing the wastewater treatment flowrate, determine the new C_out

(4 marks)

(iii) Discuss briefly the type of methanol treatment system available (3 marks)

PART C
Interplant Water Integration (20 MARKS)

You are keen to explore interplant water integration between the Kraft pulp mill with a neighbouring lignocellulose plant. The lignocellulose plant does not have concern on methanol concentration in the process water obtained from pulp mill. Instead, the efficiency of lignocellulose processing will only be affected by the total suspended solid (TSS) and pH content in the process water sources.

On an initiative to reuse water from pulp mill to lignocellulosic plant, the TSS values for unit operations in the pulp mill are measured and tabulated in
Table 2. Note that you have performed pinch analysis earlier in Part A using methanol as limiting concentration. The TSS information in Table 2 is solely prepared for Part C. The outlet streams (source and wastewater) presented the limiting TSS which you can assume independent of your solution in Part B.

Table 2: Water data in TSS for the pulp mill

The following
Table 3
summarises the water data for lignocellulosic plant.

Table 3: Water using process for lignocellulose plant

Question C6

(a) Lignocellulosic plant:

Perform water pinch analysis on lignocellulosic plant taking the total suspended solid (TSS) as the critical contaminant for water reuse/recycle. You may use either composite curve or water cascade table. The water data in Table 3 is a compilation of all water using unit processes and it is your job to decide which water limiting data to be included as part of your pinch analysis, noting that the pH will also affect the process efficiency. (6 marks)

(b) Pulp mill integrate with lignocellulosic plant:

Suggest a solution based on process integration approach to further reduce fresh water and wastewater flowrates in both pulp mill and lignocellulosic plant. Assuming only one way interplant water integration is allowed from the pulp mill to lignocellulosic plant. Report the fresh water saving base on pinch analysis (6 marks) and suggest what other practical consideration you may want to consider in doing interplant water integration (2 marks). This question is very open-ended and you should be as creative as possible in your proposal by making reasonable assumptions (2 marks) while presenting your approach. (10 marks)

(c) Interplant water network design:

Design a water network that achieves the water targets in Part C6 (b). Show clearly the fresh water streams, cross-plant pipelines and wastewater streams in a conventional block flow diagram. (4 marks)

PART D: Methanol Recovery and pH Adjustment (30 MARKS)

Question D7

(a) Boiler feed water for pulp mill (7 marks)

Let’s set the methanol and total suspended solid issue aside for a moment, and instead focus on total dissolved solid, TDS (total salts). Our site in Jamnagar is not close enough to the sea for use to desalinate seawater. Instead, we will need to use town water which is not very good. It is potable, and surprisingly has a good flavor, but for our purposes it is not very good. Town water has the following TDS concentration.

Table 4
– Contaminant Composition of Jamnagar Town Water

There is water needs in boiler to produce steam in the pulp mill. While our town water is generally good enough for methanol and TSS purposes, a second water source is needed to fulfill the hardness limit for boiler feed water. At this time, you are not doing any extra treatment except for what is needed for boiler feed water.

Using the guidelines provided in Water Engineering Rules of Thumb, your objective is to find a combination of water treatments that minimizes total water usage for making boiler feed water. Prepare a simple material balance and block flow diagram for at least ONE treatment options. You may assume 15% vent loss in the boiler system.

(b) pH adjustment for lignocellulosic plant: (6 marks)

In Part C6 (a), water integration is restricted by pH limit. Now you are given an option to adjust the pH value using H₂SO₄

(1 M). You are required to evaluate how pH adjustment would help to further reduce fresh water consumption in the lignocellulosic plant. Following table tabulates the detail components in Source 2 and Source 3.

(i) Calculate pH value in each source. Which source stream you should select to perform pH adjustment and justify your selection. (4 marks)

(ii) What is the flowrate of the source stream you should use in Lignocellulosic plant?

(2 marks)

Question D8

Assuming saturated waste steam is producing from the pulp mill at 1 bar. Your task is to recover methanol from wastewater streams by maximizing the utilization of waste steam.

(a) Simulate a methanol recovery process with Aspen using simple phase separation unit operations. Your aim is to recover as much methanol as possible to sell, setting aside the capital cost. Justify your streams selection for the methanol recovery. All selected streams are assumed available at 50 degC. Your results must include a clear material balance for each stream and report the recovery rate (%) and methanol purity (%) at each separation stage. (12 marks)

(b) Given a selling price per tonne of methanol as shown in the following table. The wastewater treatment cost is charged at $USD5/tonne of wastewater sent for treatment to the discharge limit of 100 ppm. Calculate the total revenue gain by selling the methanol product and wastewater treatment cost saving. (5 marks)